Multilayer wiring board assembly, multilayer wiring board assembly component and method of manufacture thereof

ABSTRACT

A multilayer wiring board assembly, a multilayer wiring board assembly component and a method of manufacture thereof are described in which it is possible to easily laminate together flexible FPCs having highly packing densities by via-on-via and chip-on-via. The multilayer wiring board assembly is laminated by laminating together a plurality of multilayer wiring board assembly components, each of which is made by preparing a copper plated resin film  10  made of a copper plated resin film made of a resin film having adhesivity which is provided with a copper foil bonded to one surface thereof and in which a through hole is opened through said copper foil and said resin film, and a conductive paste filler embedded by screen printing in the through hole of said copper plated resin film from said copper foil with a leading end of said conductive paste filler being projected from said resin film.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a divisional application of and claims priority to,Ser. No. 10/190,496, filed Jul. 9, 2002 now U.S. Pat. No. 6,768,064 andis based upon and claims the benefit of priority from prior JapanesePatent Application P2001-209595 filed on Jul. 10, 2001, prior JapanesePatent Application P2002-188639 filed on Jun. 27, 2002, prior JapanesePatent Application P2002-188660 filed on Jun. 27, 2002, prior JapanesePatent Application P2002-188640 filed on Jun. 27, 2002, prior JapanesePatent Application P2002-188664 filed on Jun. 27, 2002; the entirecontents of which are incorporated by reference herein.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a multilayer wiring board assemblycomposed of a plurality of printed circuit boards in a multilayeredstructure, a multilayer wiring board assembly component for use inlaminating the same and the manufacturing method of the same. Inparticular, the present invention relates to a multilayer wiring boardassembly, a multilayer wiring board assembly component for use inlaminating the same and the manufacturing method of the same, whereinthe multilayer wiring board assembly is flexible and implemented with ahighly packing density by the Flip Chip Mounting technique and so forth.

2. Description of the Related Art

A flexible printed circuit board (which is simply referred to as an“FPC” in this description) is composed of a resin film having a smallthickness for the purpose of maintaining the flexibility thereof.Because of this, in the case of such FPCs, it is essentially verydifficult to assemble a plurality of FPCs in a multilayered structure (amultilayer wiring board assembly). However, along with the advent of theimplementation of FPCs with a highly packing density, the need formultilayered structures of FPCs has increased in recent years, forexample, in consideration of the arrangement of lead wirings asconnected to flip chips mounted on FPCs. In this situation, a multilayerwiring board assembly has been manufactured by multilayering a pluralityof FPCs with an intervening glass epoxy prepreg sheet and so forthbetween each adjacent boards while one or both surface of each FPC hasbeen formed with a circuit pattern, forming holes through the entiretyof all the layers by means of a drill and the like, and interlayerinterconnecting the layers by the use of a through hall plating and thelike.

However, in the case of such a conventional method of manufacturingmultilayer wiring board assemblies by the use of a through hall plating,it is impossible to form a via hole anew on another via hole and tomount a chip on a via hole, generally called as via-on-via since a holeremains in the center of a through hall even after plating. Because ofthis, when a multilayer wiring board assembly is implemented with ahighly packing density, there are several impediments such that a leadcan not be extended from the position just below the chip whileinterlayer interconnection tends to excessively occupy a substantialarea.

On the other hand, for example, ALIVH (Any Layer Interstitial Via Hole:a registered trademark of Matsushita Electric Industrial Co., Ltd.) is arigid multilayer wiring board assembly in which via-on-via is possiblewhile a conductive paste is used for interlayer interconnection betweeneach adjacent layers. An ALIVH board is formed by repeating the processsequence including opening a through hole in an uncured resin board,filling the through hole with a conductive paste, joining a copper foilto the uncured resin board, hardening the resin while compressionbonding in order to form a multilayered structure and etching the copperfoil in order to form a circuit pattern.

However, while via-on-via is possible in the case of the manufacturingmethod as described above to form ALIVH boards since the interlayerinterconnection is made by means of a conductive paste, it is extremelydifficult to manufacture FPCs in the form of a multilayer wiring boardassembly by applying the manufacturing method to FPCs because it isnecessary to open a hole through a resin film such as a polyimide filmhaving a small thickness followed by filling up the hole with aconductive paste. This is because, when opening a hole in a resin filmhaving a small thickness, the position and the size of the hole tend tochange due to distortion of the resin film, the sucking force of a drilland the like so that the necessary accuracy of alignment is hardlyachieved during the printing operation of the conductive paste and thepositioning of the respective layers.

Also, while via-on-via is possible in the case of the manufacturingmethod making use of a conductive paste for the interlayerinterconnection like ALIVH, it is difficult to make electric connectionbetween a copper foil and a conductive paste without compromising theelectric characteristics of the copper foil and the conductive paste sothat the respective venders make use of proprietary methodsrespectively. Namely, generally speaking, when interlayerinterconnection is made by via-on-via, a copper foil and a conductivepaste are connected to each other by inserting the copper foil betweenadjacent conductive paste layers. In this case, the conductive paste isarranged to pierce the copper foil for the purpose of preservingelectric connectivity between the copper foil and the conductive pastefiller. For example, in the case of an ALIVH board, a conductive pasteis printed in order to form a projection while the thickness of theboard is reduced during thermocompression for bonding because of the useof an uncured resin board so that it becomes possible to make electricconnection of a copper foil pierced by the projection of the conductivepaste.

However, in the case of a board made of such a substance that thethickness of the board is not reduced during thermocompression forbonding, like a polyimide used for making a resin film in the case ofFPCs, the projection of a conductive paste is less effective in piecingthe copper foil. As a result, it is difficult to make electricconnection between a copper foil and a conductive paste withoutcompromising the electric characteristics.

Furthermore, in the case where a through hole is filled with aconductive paste, the conductive paste is printed in the condition thatthe surface of the conductive paste is slightly depressed since theconductive paste is pressed during printing. Because of this, there is aproblem that, even if boards having through holes filled with aconductive paste are joined to each other, it is impossible to achievesufficient electric connectivity between the fillers of the conductivepaste.

Also, while the resin film having adhesivity is contracted or expandedduring heating, the contraction or expansion can be cancelled out ifthere is a center line of symmetry in the cross section thereof.However, in the case of an adhesive layer having no center line ofsymmetry, there is observed curl in the cross section of the boardduring heating for lamination. Particularly, a polyimide film is ahighly flexuous material and therefore tends to be significantly curled.

BRIEF SUMMARY OF THE INVENTION

The present invention has been made in order to solve the shortcomingsas described above. It is an object of the present invention to providea multilayer wiring board assembly, a multilayer wiring board assemblycomponent and a method of manufacture thereof in which it is possible toeasily laminate together flexible FPCs having highly packing densitiesby via-on-via and chip-on-via.

It is another object of the present invention to provide a multilayerwiring board assembly which can be manufactured by joining multilayerwiring board assembly components to each other with a uniform pressureand therefore it is possible to fixedly laminate the multilayer wiringboard assembly with a better electric connectivity.

It is a further object of the present invention to provide a multilayerwiring board assembly which is manufactured in order that the opening ofa through hole near a copper foil is placed on a plane table having ahole of a diameter larger than that of the through hole followed byfilling the through hole with a conductive paste from a masking tape inorder to form a brim laterally extending beyond the perimeter of theopening of the copper foil, and therefore it is possible to form thebrim having a desired profile with a high degree of accuracy and havinga smaller thickness than that in the case utilzing a mask, and thereforepossible to fixedly laminate the multilayer wiring board assembly with abetter electric connectivity.

It is a still further object of the present invention to provide amultilayer wiring board assembly in which the contact area of aconductive paste filler with a copper foil is increased when compressionbonding multilayer wiring board assembly components to each other, andtherefore it is possible to improve electric connectivity.

It is a still further object of the present invention to provide amultilayer wiring board assembly in which it is possible to manufacturea multilayer wiring board assembly having a good heat resisting propertywith little damage to the respective boards during the manufacturingprocess by the use of a resin film having adhesivity made of athermosetting resin.

It is a still further object of the present invention to provide amultilayer wiring board assembly in which it is possible to manufacturea multilayer wiring board assembly having a good heat resisting propertywithout damaging the conductive resin components (the conductive paste)by the use of a resin film having adhesivity formed of a thermoplasticresin to which is given a thermosetting property.

In accordance with an aspect of the present invention, a multilayerwiring board assembly component comprises:

a copper plated resin film made of a resin film having adhesivity whichis provided with a copper foil bonded to one surface thereof and inwhich a through hole is opened through said copper foil and said resinfilm; and

a conductive paste filler embedded by screen printing in the throughhole of said copper plated resin film from said copper foil with aleading end of said conductive paste filler being projected from saidresin film.

In accordance with another aspect of the present invention, a multilayerwiring board assembly laminated with a plurality of multilayer wiringboard assembly components, at least one of said multilayer wiring boardassembly components comprises:

a copper plated resin film made of a resin film having adhesivity whichis provided with a copper foil bonded to one surface thereof and inwhich a through hole is opened through said copper foil and said resinfilm; and

a conductive paste filler embedded by screen printing in the throughhole of said copper plated resin film from said copper foil with aleading end of said conductive paste filler being projected from saidresin film,

wherein the leading end of said conductive paste filler of said at leastone of said multilayer wiring board assembly components makes electriccontact with the copper foil or the conductive paste filler of anadjacent one of said multilayer wiring board assembly components.

In accordance with a further aspect of the present invention, amanufacturing method of a multilayer wiring board assembly componentcomprises:

a step of forming a through hole in a copper plated resin film made of aresin film having adhesivity which is provided with a copper foil bondedto one surface thereof and in which said through hole is opened throughsaid copper foil and said resin film; and

a step of embedding a conductive paste filler by screen printing in thethrough hole of said copper plated resin film from said copper foil witha leading end of said conductive paste filler being projected from saidresin film.

In accordance with a still further aspect of the present invention, amanufacturing method of a multilayer wiring board assembly componentcomprises:

a step of etching a copper plated resin film made of a resin film havingadhesivity which is provided with a copper foil bonded to one surfacethereof in order to form a predetermined circuit pattern;

a step of forming a mask layer on said resin film of the copper platedresin film having been formed with said circuit pattern;

a step of forming a through hole opened through said copper foil, saidresin film and said mask layer;

a step of embedding a conductive paste filler by screen printing in thethrough hole of said copper plated resin film from said copper foil; and

a step of removing said mask layer.

In accordance with a still further aspect of the present invention, in amanufacturing method of a multilayer wiring board assembly laminatedwith a plurality of multilayer wiring board assembly components, atleast one of said multilayer wiring board assembly components comprises:

a copper plated resin film made of a resin film having adhesivity whichis provided with a copper foil bonded to one surface thereof and inwhich a through hole is opened through said copper foil and said resinfilm; and

a conductive paste filler embedded by screen printing in the throughhole of said copper plated resin film from said copper foil with aleading end of said conductive paste filler being projected from saidresin film,

wherein said multilayer wiring board assembly is laminated with aplurality of said multilayer wiring board assembly components throughsaid resin film in order that the leading end of said conductive pastefiller of said at least one of said multilayer wiring board assemblycomponents makes electric contact with said copper foil or saidconductive paste filler of an adjacent one of said multilayer wiringboard assembly components.

In accordance with a still further aspect of the present invention, amultilayer wiring board assembly component comprises:

a copper plated resin film made of a resin film having adhesivity whichis provided with a copper foil bonded to one surface thereof and inwhich a through hole is opened through said copper foil and said resinfilm; and

a conductive paste filler embedded in the through hole of said copperplated resin film from said copper foil with a leading end of saidconductive paste filler being projected from said resin film.

In accordance with a still further aspect of the present invention, amanufacturing method of a multilayer wiring board assembly componentcomprises:

a step of forming a through hole in a copper plated resin film made of aresin film having adhesivity which is provided with a copper foil bondedto one surface thereof and in which said through hole is opened throughsaid copper foil and said resin film; and

a step of embedding a conductive paste filler in the through hole fromsaid copper foil with a leading end of said conductive paste fillerbeing projected from said resin film.

In accordance with a still further aspect of the present invention, amultilayer wiring board assembly component comprises:

a copper plated resin film made of a resin film having adhesivity whichis provided with a copper foil bonded to one surface thereof and inwhich a through hole is opened through said copper foil and said resinfilm; and

a conductive paste filler embedded in the through hole of said copperplated resin film with one end of said conductive paste filler beingprojected from said resin film and the tail end of said conductive pastefiller being projected to the same height as said copper foil.

In accordance with a still further aspect of the present invention, amultilayer wiring board assembly component comprises:

a copper plated resin film made of a resin film having adhesivity whichis provided with a copper foil bonded to one surface thereof and inwhich a through hole is opened through said copper foil and said resinfilm; and

a conductive paste filler embedded by screen printing in the throughhole of said copper plated resin film from said copper foil with aleading end of said conductive paste filler being projected from saidresin film and with part of said conductive paste being laterallyextending beyond the perimeter of the opening of the through hole ofsaid copper foil.

In accordance with a still further aspect of the present invention, amultilayer wiring board assembly laminated with a plurality ofmultilayer wiring board assembly components, the most outer layer ofsaid multilayer wiring board assembly components comprises:

a copper plated resin film made of a resin film having adhesivity whichis provided with a copper foil bonded to one surface thereof and inwhich a through hole is opened through said copper foil and said resinfilm; and

a conductive paste filler embedded in the through hole of said copperplated resin film from said copper foil with one end of said conductivepaste filler being projected from said resin film and the tail end ofsaid conductive paste filler being projected to the same height as saidcopper foil,

wherein the leading end of said conductive paste filler of said mostouter multilayer wiring board assembly components makes electric contactwith said copper foil or said conductive paste filler of an adjacent oneof said multilayer wiring board assembly components.

In accordance with a still further aspect of the present invention, amultilayer wiring board assembly laminated with a plurality ofmultilayer wiring board assembly components includes:

a first multilayer wiring board assembly component comprising a copperplated resin film made of a resin film having adhesivity which isprovided with a copper foil bonded to one surface thereof and in which athrough hole is opened through said copper foil and said resin film, anda conductive paste filler embedded in the through hole of said copperplated resin film from said copper foil with a leading end of saidconductive paste filler being projected from said resin film and withpart of said conductive paste being laterally extending beyond theperimeter of the opening of the through hole of said copper foil; and

a second multilayer wiring board assembly component comprising a copperplated resin film made of a resin film having adhesivity which isprovided with a copper foil bonded to one surface thereof and in which athrough hole is opened through said copper foil and said resin film, anda conductive paste filler embedded in the through hole of said copperplated resin film from said copper foil with a leading end of saidconductive paste filler being projected from said resin film and thetail end of said conductive paste filler being projected to the sameheight as said copper foil,

wherein said second multilayer wiring board assembly component islocated as the most outer layer of the multilayer wiring board assemblywhile said first multilayer wiring board assembly component is locatedas an inner layer of the multilayer wiring board assembly other thansaid second multilayer wiring board assembly, and wherein the leadingend of said conductive paste filler of one of said multilayer wiringboard assembly components makes electric contact with said copper foilor said conductive paste filler of an adjacent one of said multilayerwiring board assembly components.

In accordance with a still further aspect of the present invention, amanufacturing method of a multilayer wiring board assembly laminatedwith a plurality of multilayer wiring board assembly componentsincludes:

a first multilayer wiring board assembly component comprising a copperplated resin film made of a resin film having adhesivity which isprovided with a copper foil bonded to one surface thereof and in which athrough hole is opened through said copper foil and said resin film, anda conductive paste filler embedded in the through hole of said copperplated resin film from said copper foil with a leading end of saidconductive paste filler being projected from said resin film and withpart of said conductive paste being laterally extending beyond theperimeter of the opening of the through hole of said copper foil; and

a second multilayer wiring board assembly component comprising a copperplated resin film made of a resin film having adhesivity which isprovided with a copper foil bonded to one surface thereof and in which athrough hole is opened through said copper foil and said resin film, anda conductive paste filler embedded in the through hole of said copperplated resin film from said copper foil with a leading end of saidconductive paste filler being projected from said resin film and thetail end of said conductive paste filler being projected to the sameheight as said copper foil,

wherein said second multilayer wiring board assembly component islocated as the most outer layer of the multilayer wiring board assemblywhile said first multilayer wiring board assembly component is locatedas an inner layer of the multilayer wiring board assembly other thansaid second multilayer wiring board assembly, and wherein saidmultilayer wiring board assembly is laminated with a plurality of saidmultilayer wiring board assembly components through said resin film inorder that the leading end of said conductive paste filler of saidmultilayer wiring board assembly components makes electric contact withsaid copper foil or said conductive paste filler of an adjacent one ofsaid multilayer wiring board assembly components.

In accordance with a still further aspect of the present invention, amanufacturing method of a multilayer wiring board assembly componentcomprises:

a step of forming a through hole in a copper plated resin film made of aresin film having adhesivity which is provided with a copper foil bondedto one surface thereof and in which said through hole is opened throughsaid copper foil and said resin film; and

a step of embedding a conductive paste filler in the through hole ofsaid copper plated resin film from said copper foil with a leading endof said conductive paste filler being projected from said resin film andthe tail end of said conductive paste filler being projected to the sameheight as said copper foil.

In accordance with a still further aspect of the present invention, amanufacturing method of a multilayer wiring board assembly componentcomprises:

a step of forming a mask layer on an adhesive layer bonded to onesurface of a copper plated resin film made of a resin film havingadhesivity which is provided with a copper foil bonded to the othersurface thereof;

a step of forming a through hole opened through said copper foil, saidresin film and said mask layer;

a step of embedding a conductive paste filler in the through hole withthe tail end of said conductive paste filler being located at the sameheight as said copper foil; and

a step of removing said mask layer to leave the tail end of saidconductive paste filler being projected from said resin film.

In accordance with a still further aspect of the present invention, amanufacturing method of a multilayer wiring board assembly componentcomprises:

a step of forming a through hole in a copper plated resin film made of aresin film having adhesivity which is provided with a copper foil bondedto one surface thereof and in which said through hole is opened throughsaid copper foil and said resin film; and

a step of embedding a conductive paste filler by screen printing in thethrough hole of said copper plated resin film from said copper foil witha leading end of said conductive paste filler being projected from saidresin film with part of said conductive paste being laterally extendingbeyond the perimeter of the opening of the through hole of said copperfoil.

In accordance with a still further aspect of the present invention, amanufacturing method of a multilayer wiring board assembly componentcomprises:

a step of etching a copper plated resin film made of a resin film havingadhesivity which is provided with a copper foil bonded to one surfacethereof in order to form a predetermined circuit pattern;

a step of forming a mask layer on said resin film of the copper platedresin film having been formed with said circuit pattern;

a step of forming a through hole opened through said copper foil, saidresin film and said mask layer;

a step of embedding a conductive paste filler by screen printing in thethrough hole of said copper plated resin film from said copper foil withpart of said conductive paste being laterally extending beyond theperimeter of the opening of the through hole of said copper foil; and

a step of removing said mask layer to leave the tail end of saidconductive paste filler being projected from said resin film.

In accordance with a still further aspect of the present invention, amanufacturing method of a multilayer wiring board assembly componentcomprises:

a step of etching a copper plated resin film made of a resin film havingadhesivity which is provided with a copper foil bonded to one surfacethereof in order to form a predetermined circuit pattern;

a step of forming a mask layer on said resin film of the copper platedresin film having been formed with said circuit pattern;

a step of forming a through hole opened through said copper foil, saidresin film and said mask layer;

a step of placing, on said copper foil over said through hole, a mask ofa thickness larger than that of said through hole;

a step of embedding a conductive paste filler in said through hole withthe tail end of said conductive paste filler being located at the sameheight as said mask;

a step of removing said mask to leave said tail end of said conductivepaste filler being projected from said copper foil with part of saidconductive paste being laterally extending beyond the perimeter of theopening of the through hole of said copper foil; and

a step of removing said mask to leave the tail end of said conductivepaste filler being projected from said resin film.

In accordance with a still further aspect of the present invention, in amultilayer wiring board assembly laminated with a plurality ofmultilayer wiring board assembly components, at least one of saidmultilayer wiring board assembly components is manufactured by:

a step of etching a copper plated resin film made of a resin film havingadhesivity which is provided with a copper foil bonded to one surfacethereof in order to form a predetermined circuit pattern;

a step of forming a mask layer on said resin film of the copper platedresin film having been formed with said circuit pattern;

a step of forming a through hole opened through said copper foil, saidresin film and said mask layer;

a step of placing, on said copper foil over said through hole, a mask ofa thickness larger than that of said through hole;

a step of embedding a conductive paste filler in said through hole withthe tail end of said conductive paste filler being located at the sameheight as said mask;

a step of removing said mask to leave said tail end of said conductivepaste filler being projected from said copper foil with part of saidconductive paste being laterally extending beyond the perimeter of theopening of the through hole of said copper foil; and

a step of removing said mask to leave the tail end of said conductivepaste filler being projected from said resin film,

wherein the leading end of said conductive paste filler of said at leastone of said multilayer wiring board assembly components makes electriccontact with said copper foil or said conductive paste filler of anadjacent one of said multilayer wiring board assembly components.

In accordance with a still further aspect of the present invention, in amanufacturing method of a multilayer wiring board assembly laminatedwith a plurality of multilayer wiring board assembly components, atleast one of said multilayer wiring board assembly components ismanufactured by:

a step of etching a copper plated resin film made of a resin film havingadhesivity which is provided with a copper foil bonded to one surfacethereof in order to form a predetermined circuit pattern;

a step of forming a mask layer on said resin film of the copper platedresin film having been formed with said circuit pattern;

a step of forming a through hole opened through said copper foil, saidresin film and said mask layer;

a step of placing, on said copper foil over said through hole, a mask ofa thickness larger than that of said through hole;

a step of embedding a conductive paste filler in said through hole withthe tail end of said conductive paste filler being located at the sameheight as said mask;

a step of removing said mask to leave said tail end of said conductivepaste filler being projected from said copper foil with part of saidconductive paste being laterally extending beyond the perimeter of theopening of the through hole of said copper foil; and

a step of removing said mask to leave the tail end of said conductivepaste filler being projected from said resin film,

wherein said multilayer wiring board assembly is laminated with aplurality of said multilayer wiring board assembly components throughsaid resin film in order that the leading end of said conductive pastefiller of said at least one of said multilayer wiring board assemblycomponents makes electric contact with said copper foil or saidconductive paste filler of an adjacent one of said multilayer wiringboard assembly components.

In accordance with a still further aspect of the present invention, amanufacturing method of a multilayer wiring board assembly componentcomprises:

a step of etching a copper plated resin film made of a resin film havingadhesivity which is provided with a copper foil bonded to one surfacethereof in order to form a predetermined circuit pattern;

a step of forming a mask layer on said resin film of the copper platedresin film having been formed with said circuit pattern;

a step of forming a through hole opened through said copper foil, saidresin film and said mask layer;

a step of placing said copper plated resin film on a plane table inwhich a hole is opened with a thickness larger than that of said throughhole in order that said copper foil is located in a lower position withthe through hole located over the hole of said plane table;

a step of embedding a conductive paste filler by screen printing in thethrough hole of said copper plated resin film from said mask layer witha leading end of said conductive paste filler being projected from saidcopper foil with part of said conductive paste being laterally extendingbeyond the perimeter of the opening of the through hole of said copperfoil; and

a step of removing said mask layer to leave the leading end of saidconductive paste filler being projected from said resin film.

In accordance with a still further aspect of the present invention, in amultilayer wiring board assembly laminated with a plurality ofmultilayer wiring board assembly components, at least one of saidmultilayer wiring board assembly components is manufactured by:

a step of etching a copper plated resin film made of a resin film havingadhesivity which is provided with a copper foil bonded to one surfacethereof in order to form a predetermined circuit pattern;

a step of forming a mask layer on said resin film of the copper platedresin film having been formed with said circuit pattern;

a step of forming a through hole opened through said copper foil, saidresin film and said mask layer;

a step of placing said copper plated resin film on a plane table inwhich a hole is opened with a thickness larger than that of said throughhole in order that said copper foil is located in a lower position withthe through hole located over the hole of said plane table;

a step of embedding a conductive paste filler in the through hole ofsaid copper plated resin film from said mask layer with a leading end ofsaid conductive paste filler being projected from said copper foil withpart of said conductive paste being laterally extending beyond theperimeter of the opening of the through hole of said copper foil; and

a step of removing said mask layer to leave the tail end of saidconductive paste filler being projected from said resin film,

wherein said tail end of said conductive paste filler of said at leastone of said multilayer wiring board assembly components makes electriccontact with said copper foil or said conductive paste filler of anadjacent one of said multilayer wiring board assembly components.

In accordance with a still further aspect of the present invention, in amanufacturing method of a multilayer wiring board assembly laminatedwith a plurality of multilayer wiring board assembly components, atleast one of said multilayer wiring board assembly components ismanufactured by:

a step of etching a copper plated resin film made of a resin film havingadhesivity which is provided with a copper foil bonded to one surfacethereof in order to form a predetermined circuit pattern;

a step of forming a mask layer on said resin film of the copper platedresin film having been formed with said circuit pattern;

a step of forming a through hole opened through said copper foil, saidresin film and said mask layer;

a step of placing said copper plated resin film on a plane table inwhich a hole is opened with a thickness larger than that of said throughhole in order that said copper foil is located in a lower position withthe through hole located over the hole of said plane table;

a step of embedding a conductive paste filler in the through hole ofsaid copper plated resin film from said mask layer with a leading end ofsaid conductive paste filler being projected from said copper foil withpart of said conductive paste being laterally extending beyond theperimeter of the opening of the through hole of said copper foil; and

a step of removing said mask layer to leave the tail end of saidconductive paste filler being projected from said resin film,

wherein said multilayer wiring board assembly is laminated with aplurality of said multilayer wiring board assembly components throughsaid resin film in order that said tail end of said conductive pastefiller of said at least one of said multilayer wiring board assemblycomponents makes electric contact with said copper foil or saidconductive paste filler of an adjacent one of said multilayer wiringboard assembly components.

In accordance with a still further aspect of the present invention, amultilayer wiring board assembly component comprises:

a copper plated resin film made of a resin film having adhesivity whichis provided with a copper foil bonded to one surface thereof and inwhich a through hole is opened through said copper foil and said resinfilm; and

a conductive paste filler embedded in the through hole of said copperplated resin film from said copper foil with a leading end of saidconductive paste filler being projected from said resin film and withthe tail end of said conductive paste filler being projected from saidcopper foil.

In accordance with a still further aspect of the present invention, in amultilayer wiring board assembly laminated with a plurality ofmultilayer wiring board assembly components, at least one of saidmultilayer wiring board assembly components comprises:

a copper plated resin film made of a resin film having adhesivity whichis provided with a copper foil bonded to one surface thereof and inwhich a through hole is opened through said copper foil and said resinfilm; and

a conductive paste filler embedded in the through hole of said copperplated resin film from said copper foil with a leading end of saidconductive paste filler being projected from said resin film and withthe tail end of said conductive paste filler being projected from saidcopper foil,

wherein the leading end of said conductive paste filler of said at leastone of said multilayer wiring board assembly components makes electriccontact with said copper foil or said conductive paste filler of anadjacent one of said multilayer wiring board assembly components.

In accordance with a still further aspect of the present invention, in amultilayer wiring board assembly laminated with a plurality ofmultilayer wiring board assembly components, at least one of saidmultilayer wiring board assembly components comprises:

a copper plated resin film made of a resin film having adhesivity whichis provided with a copper foil bonded to one surface thereof and inwhich a through hole is opened through said copper foil and said resinfilm; and

a conductive paste filler embedded in the through hole of said copperplated resin film from said copper foil with a leading end of saidconductive paste filler being projected from said resin film and withthe tail end of said conductive paste filler being projected from saidcopper foil,

wherein said multilayer wiring board assembly is laminated with aplurality of said multilayer wiring board assembly components throughsaid resin film in order that the leading end of said conductive pastefiller of said at least one of said multilayer wiring board assemblycomponents makes electric contact with said copper foil or saidconductive paste filler of an adjacent one of said multilayer wiringboard assembly components.

In accordance with a still further aspect of the present invention, amanufacturing method of a multilayer wiring board assembly componentcomprises:

a step of forming a through hole in a copper plated resin film made of aresin film having adhesivity which is provided with a copper foil bondedto one surface thereof and in which said through hole is opened throughsaid copper foil and said resin film; and

a step of embedding a conductive paste filler in the through hole ofsaid copper plated resin film from said copper foil with a leading endof said conductive paste filler being projected from said resin filmwith the tail end of said conductive paste filler being projected fromsaid copper foil.

In accordance with a still further aspect of the present invention, amanufacturing method of a multilayer wiring board assembly componentcomprises:

a step of preparing a copper plated resin film made of a resin filmhaving adhesivity which is provided with a copper foil bonded to onesurface thereof and forming first and second mask layers on said onesurface and the other surface opposed to said one surface of said copperplated resin film;

a step of forming a through hole opened through said copper foil, saidresin film and said first and second mask layers;

a step of embedding a conductive paste filler in said through hole withthe leading and tail ends of said conductive paste filler being locatedat the same height as said mask layers; and

a step of removing said first and second mask layers to leave theleading end of said conductive paste filler being projected from saidresin film with the tail end of said conductive paste filler beingprojected from said copper foil.

In accordance with a still further aspect of the present invention, amultilayer wiring board assembly component comprises:

a copper plated resin film made of a thermosetting resin film havingadhesivity which is provided with a copper foil bonded to one surfacethereof and in which a through hole is opened through said copper foiland said resin film; and

a conductive paste filler embedded in the through hole of said copperplated resin film from said copper foil with a leading end of saidconductive paste filler being projected from said resin film.

In accordance with a still further aspect of the present invention, in amultilayer wiring board assembly laminated with a plurality ofmultilayer wiring board assembly components, at least one of saidmultilayer wiring board assembly components comprises:

a copper plated resin film made of a thermosetting resin film havingadhesivity which is provided with a copper foil bonded to one surfacethereof and in which a through hole is opened through said copper foiland said resin film; and

a conductive paste filler embedded in the through hole of said copperplated resin film from said copper foil with a leading end of saidconductive paste filler being projected from said resin film,

wherein the leading end of said conductive paste filler of said at leastone of said multilayer wiring board assembly components makes electriccontact with said copper foil or said conductive paste filler of anadjacent one of said multilayer wiring board assembly components.

In accordance with a still further aspect of the present invention, amanufacturing method of a multilayer wiring board assembly componentcomprises:

a step of forming a through hole in a copper plated resin film made of athermosetting resin film having adhesivity which is provided with acopper foil bonded to one surface thereof and in which said through holeis opened through said copper foil and said resin film; and

a step of embedding a conductive paste filler in the through hole ofsaid copper plated resin film from said copper foil with a leading endof said conductive paste filler being projected from said resin film.

In accordance with a still further aspect of the present invention, amanufacturing method of a multilayer wiring board assembly componentcomprises:

a step of etching a copper plated resin film made of a thermosettingresin film having adhesivity which is provided with a copper foil bondedto one surface thereof in order to form a predetermined circuit pattern;

a step of forming a mask layer on said resin film of the copper platedresin film having been formed with said circuit pattern;

a step of forming a through hole opened through said copper foil, saidresin film and said mask layer;

a step of embedding a conductive paste filler in the through hole ofsaid copper plated resin film from said copper foil; and

a step of removing said mask layer.

In accordance with a still further aspect of the present invention, amultilayer wiring board assembly laminated with a plurality ofmultilayer wiring board assembly components, at least one of saidmultilayer wiring board assembly components comprises:

a copper plated resin film made of a thermosetting resin film havingadhesivity which is provided with a copper foil bonded to one surfacethereof and in which a through hole is opened through said copper foiland said resin film; and

a conductive paste filler embedded in the through hole of said copperplated resin film from said copper foil with a leading end of saidconductive paste filler being projected from said resin film,

wherein said multilayer wiring board assembly is laminated with aplurality of said multilayer wiring board assembly components throughsaid resin film in order that the leading end of said conductive pastefiller of said at least one of said multilayer wiring board assemblycomponents makes electric contact with said copper foil or saidconductive paste filler of an adjacent one of said multilayer wiringboard assembly components.

In accordance with a still further aspect of the present invention, amultilayer wiring board assembly component comprises:

a copper plated resin film made of a thermosetting resin film havingadhesivity and which is provided with a copper foil bonded to onesurface thereof and in which a through hole is opened through saidcopper foil and said resin film; and

a conductive paste filler embedded in the through hole of said copperplated resin film from said copper foil with a leading end of saidconductive paste filler being projected from said resin film.

In accordance with a still further aspect of the present invention, amultilayer wiring board assembly laminated with a plurality ofmultilayer wiring board assembly components, at least one of saidmultilayer wiring board assembly components comprises:

a copper plated resin film made of a resin film to which is given athermosetting property and which is provided with a copper foil bondedto one surface thereof and in which a through hole is opened throughsaid copper foil and said resin film; and

a conductive paste filler embedded in the through hole of said copperplated resin film from said copper foil with a leading end of saidconductive paste filler being projected from said resin film,

wherein the leading end of said conductive paste filler of said at leastone of said multilayer wiring board assembly components makes electriccontact with said copper foil or said conductive paste filler of anadjacent one of said multilayer wiring board assembly components.

In accordance with a still further aspect of the present invention, amanufacturing method of a multilayer wiring board assembly componentcomprises:

a step of forming a through hole in a copper plated resin film made of aresin film to which is given a thermosetting property and which isprovided with a copper foil bonded to one surface thereof and in whichsaid through hole is opened through said copper foil and said resinfilm; and

a step of embedding a conductive paste filler in the through hole ofsaid copper plated resin film from said copper foil with a leading endof said conductive paste filler being projected from said resin film.

In accordance with a still further aspect of the present invention, amanufacturing method of a multilayer wiring board assembly componentcomprises:

a step of etching a copper plated resin film made of a resin film towhich is given a thermosetting property and which is provided with acopper foil bonded to one surface thereof in order to form apredetermined circuit pattern;

a step of forming a mask layer on said resin film of the copper platedresin film having been formed with said circuit pattern;

a step of forming a through hole opened through said copper foil, saidresin film and said mask layer;

a step of embedding a conductive paste filler by screen printing in thethrough hole of said copper plated resin film from said copper foil; and

a step of removing said mask layer.

In accordance with a still further aspect of the present invention, in amanufacturing method of a multilayer wiring board assembly laminatedwith a plurality of multilayer wiring board assembly components, atleast one of said multilayer wiring board assembly components comprises:

a copper plated resin film made of a resin film to which is given athermosetting property and which is provided with a copper foil bondedto one surface thereof and in which a through hole is opened throughsaid copper foil and said resin film; and

a conductive paste filler embedded in the through hole of said copperplated resin film from said copper foil with a leading end of saidconductive paste filler being projected from said resin film,

wherein said multilayer wiring board assembly is laminated with saidresin film having adhesivity by thermocompression at about 180° C. inorder that said leading end of said conductive paste filler of said atleast one of said multilayer wiring board assembly components makeselectric contact with said copper foil or said conductive paste fillerof an adjacent one of said multilayer wiring board assembly components.

BRIEF DESCRIPTION OF DRAWINGS

The aforementioned and other features and objects of the presentinvention and the manner of attaining them will become more apparent andthe invention itself will be best understood by reference to thefollowing description of a preferred embodiment taken in conjunctionwith the accompanying drawings, wherein:

FIG. 1 shows cross sectional views of the intermediate structures of amultilayer wiring board assembly component for use in manufacturing amultilayer wiring board assembly in accordance with an embodiment of thepresent invention in the order of the manufacturing steps.

FIG. 2 shows cross sectional views showing the multilayer wiring boardassembly in accordance with the embodiment of the present invention inthe order of the manufacturing steps.

FIG. 3 shows cross sectional views showing the multilayer wiring boardassembly in accordance with the embodiment of the present invention inthe order of the manufacturing steps.

FIG. 4 shows cross sectional views of an exemplary connection terminalstructure of the multilayer wiring board assembly in accordance with anembodiment of the present invention.

FIG. 5 shows cross sectional views of another exemplary connectionterminal structure of the multilayer wiring board assembly in accordancewith an embodiment of the present invention.

FIG. 6 shows cross sectional views of a further exemplary connectionterminal structure of the multilayer wiring board assembly in accordancewith an embodiment of the present invention.

FIG. 7 shows cross sectional views of the intermediate structures of afirst multilayer wiring board assembly component for use inmanufacturing a multilayer wiring board assembly in accordance with afurther embodiment of the present invention in the order of themanufacturing steps.

FIG. 8 shows cross sectional views of the intermediate structures of asecond multilayer wiring board assembly component for use inmanufacturing a multilayer wiring board assembly in accordance with thefurther embodiment of the present invention in the order of themanufacturing steps.

FIG. 9 shows cross sectional views of the intermediate structures of asecond multilayer wiring board assembly component for use inmanufacturing a multilayer wiring board assembly in accordance with anstill further embodiment of the present invention in the order of themanufacturing steps.

FIG. 10 shows cross sectional views showing the multilayer wiring boardassembly in accordance with a still further embodiment of the presentinvention in the order of the manufacturing steps.

FIG. 11 shows cross sectional views showing the multilayer wiring boardassembly in accordance with the still further embodiment of the presentinvention in the order of the manufacturing steps.

FIG. 12 shows cross sectional views of the intermediate structures of amultilayer wiring board assembly component for use in manufacturing amultilayer wiring board assembly in accordance with the still furtherembodiment of the present invention in the order of the manufacturingsteps.

FIG. 13 shows cross sectional views showing the multilayer wiring boardassembly in accordance with the still further embodiment of the presentinvention in the order of the manufacturing steps.

FIG. 14 shows cross sectional views showing the multilayer wiring boardassembly in accordance with the still further embodiment of the presentinvention in the order of the manufacturing steps.

FIG. 15 shows cross sectional views of the intermediate structures of amultilayer wiring board assembly component for use in manufacturing amultilayer wiring board assembly in accordance with a still furtherembodiment of the present invention in the order of the manufacturingsteps.

FIG. 16 shows cross sectional views showing the multilayer wiring boardassembly in accordance with the still further embodiment of the presentinvention in the order of the manufacturing steps.

FIG. 17 shows cross sectional views showing the multilayer wiring boardassembly in accordance with the still further embodiment of the presentinvention in the order of the manufacturing steps.

FIG. 18 shows cross sectional views of the intermediate structures of amultilayer wiring board assembly component for use in manufacturing amultilayer wiring board assembly in accordance with a still furtherembodiment of the present invention in the order of the manufacturingsteps.

FIG. 19 shows cross sectional views showing the multilayer wiring boardassembly in accordance with the still further embodiment of the presentinvention in the order of the manufacturing steps.

FIG. 20 shows cross sectional views showing the multilayer wiring boardassembly in accordance with the still further embodiment of the presentinvention in the order of the manufacturing steps.

FIG. 21 shows cross sectional views of the intermediate structures of amultilayer wiring board assembly component for use in manufacturing amultilayer wiring board assembly in accordance with a still furtherembodiment of the present invention in the order of the manufacturingsteps.

FIG. 22 shows cross sectional views showing the multilayer wiring boardassembly in accordance with the still further embodiment of the presentinvention in the order of the manufacturing steps.

FIG. 23 shows cross sectional views showing the multilayer wiring boardassembly in accordance with the still further embodiment of the presentinvention in the order of the manufacturing steps.

FIG. 24 shows cross sectional views of the intermediate structures of amultilayer wiring board assembly component for use in manufacturing amultilayer wiring board assembly in accordance with a still furtherembodiment of the present invention in the order of the manufacturingsteps.

FIG. 25 shows cross sectional views showing the multilayer wiring boardassembly in accordance with the still further embodiment of the presentinvention in the order of the manufacturing steps.

FIG. 26 shows cross sectional views showing the multilayer wiring boardassembly in accordance with the still further embodiment of the presentinvention in the order of the manufacturing steps.

DETAILED DESCRIPTION OF THE INVENTION

In the followings, various preferred embodiments of the presentinvention will be described with reference to the accompanying drawings.

FIG. 1 shows cross sectional views of the intermediate structures of amultilayer wiring board assembly component for use in manufacturing amultilayer wiring board assembly in accordance with an embodiment of thepresent invention in the order of the manufacturing steps. FIG. 2 andFIG. 3 are cross sectional views showing the multilayer wiring boardassembly in accordance with the embodiment of the present invention inthe order of the manufacturing steps.

The multilayer wiring board assembly component 20 is a connection unitfor use in the process of laminating a multilayer wiring board assemblyand comprises an FPC as a base element made of a single sided copperplated resin film. Namely, as illustrated in FIG. 1(i), the multilayerwiring board assembly component 20 is composed of a copper plated resinfilm 10 composed of a flexible resin film 1 having adhesivity and madeof a thermoplastic polyimide (TPI) and the like and provided with acopper foil 2 bonded to one surface thereof, and a conductive pastefiller 8 embedded in a through hole 7 (refer to FIG. 1(g)) passedthrough the resin film 10 to form an inner via hole. A predeterminedcircuit pattern is formed in the copper foil 2 by etching and the like.The conductive paste filler 8 is embedded in the through hole 7 from thesurface of the copper foil 2 by screen printing and so forth with a brimformed laterally extending on the upper surface of the copper foil 2beyond the perimeter of the opening thereof in order that the leadingend thereof is projected through the opposed surface of the copperplated resin film 10 having the resin film 1.

A multilayer wiring board assembly is laminated by stacking a pluralityof the multilayer wiring board assembly components as illustrated inFIG. 1(i) (three units in the case of the embodiment as illustrated inFIG. 2 and FIG. 3). As illustrated in FIG. 2 and FIG. 3, since thethrough hole 7 of the multilayer wiring board assembly component isfilled with the conductive paste filler 8, it is possible to makeinterlayer connection via-on-via.

Also, as illustrated in FIG. 1(i), the conductive paste filler 8 isprinted in order that a projection is formed in the surface opposed tothe printing surface. Meanwhile, the height of the projection of theconductive paste filler 8 depends on the size of the recess and ispreferably 10 micrometer or thereabout.

In this manner, when the interlayer interconnection is made byvia-on-via, the conductive paste fillers 8 are connected directly toeach other rather than through an intervening copper foil therebetween.

Also, as illustrated in FIG. 1(h), the conductive paste filler 8 isembedded in the opening 5 in order to make electric contact with theinner side surface and the upper surface of the copper foil 2 beyond theperimeter of the opening 5 thereof since the printing surface of theconductive paste filler 8 is extended laterally beyond the surface ofthe copper foil 2 (while sometimes indented slightly lower than thesurface of the brim 8 a) after the filing printing operation.

Next, the manufacturing process (method) of the multilayer wiring boardassembly in accordance with the present invention will be explained withreference to FIG. 1 through FIG. 3.

(1) The Manufacturing Process of a Multilayer Wiring Board AssemblyComponent (FIG. 1):

At first, as illustrated in FIG. 1(a), a single sided copper platedresin film 10 is provided or prepared as the resin film 1 made of athermoplastic polyimide (TPI) having a thickness of 30 to 100 micrometerwith the copper foil 2 having a thickness of 5 to 18 micrometer bondedto one surface.

Next, as illustrated in FIG. 1(b), a dry film (resist) 4 is laminated tothe copper foil 2 bonded to the resin film 1 with a vacuum laminator ora roll laminator. Next, as illustrated in FIG. 1(c), the dry film 4 isexposed to radiation of a circuit pattern followed by developing the dryfilm 4.

Next, as illustrated in FIG. 1(d), a predetermined circuit pattern isformed by etching the copper foil 2 with the dry film 4 as a mask. Inthis step, the opening 5 is formed by the same etching process for usein the subsequent step of opening the through hole 7. Next, after thedry film 4 is removed from the copper foil 2 as illustrated in FIG.1(e), a masking tape 6 having a thickness of 10 to 50 micrometer isbonded as a mask to the surface of the resin film 1 as opposed to thecopper foil 2 as illustrated in FIG. 1(f). The masking tape 6 may bemade of a PET and the like. Alternatively, a resin film can be used forthe same purpose in place of the masking tape.

Next, as illustrated in FIG. 1(g), the through hole 7 of 0.05 to 0.3 mmdiameter is opened in the resin film 1 through the resin film 1 and themasking tape 6 by exposing them to a laser light through the opening 5by means of a CO₂ laser and the like. Meanwhile, the through hole 7 maybe opened by means of a drill in place of the laser exposure process.

Next, as illustrated in FIG. 1(h), a conductive paste is screen printedto fill the through hole 7 with the conductive paste filler 8. At thistime, the conductive paste filler 8 is screen printed with a diameterlarger than the opening 5 (the through hole 7) by a factor of about 1.1to 2.0 so that part of the conductive paste remains on the upper surfaceof the copper foil 2 beyond the perimeter of the opening 5 thereof. Bythis configuration, there is formed the brim 8 a which is connected tothe land surface 2 a of the copper foil 2 in the direction normal to thesurface. Meanwhile, Ag, Cu, C, Cu coated with Ag and other conductivepastes can be used to form the conductive paste filler 8.

Next, the projection 8 b of the conductive paste filler 8 which isprojecting through the resin film 1 in the surface opposed to theprinting surface is formed by heating the conductive paste filler 8 inan oven at 80° C. for an hour to partially cure the conductive pastefiller 8 and removing the masking tape 6 as illustrated in FIG. 1(i). Bythis process, the multilayer wiring board assembly component 20 iscompletely formed.

(2) The Press Process of the Multilayer Wiring Board Assembly (FIG. 2and FIG. 3):

As illustrated in FIGS. 2(a), (b) and (c), a plurality of circuitpatterns and a plurality of through holes 7 are formed on each of themultilayer wiring board assembly components (three multilayer wiringboard assembly components) 20 a, 20 b and 20 c. Also, the through holes7 are filled with the conductive paste fillers 8.

The formation of the multilayer wiring board assembly 30 in accordancewith the present embodiment is completed by laminating together therespective multilayer wiring board assembly components 20 a to 20 c asillustrated in FIG. 3(a) by thermocompression with a most outer copperfoil 9 at the same time and forming a circuit on the most outer copperfoil 9 as illustrated in FIG. 3(b). The step of laminating therespective multilayer wiring board assembly components 20 a to 20 c andthe most outer copper foil 9 to each other by thermocompression iscarried out by heating them at 280° C. or thereabout and pressing themat 9 MPa or thereabout in order to embed the circuit pattern of thecopper foil 2 and the brim 8 a of the conductive paste filler 8 in theresin film 1 made of a thermoplastic polyimide having adhesivity andfluidity. At this time, the copper foil 2 opposed to the copper foil 9as the outermost layer and the brim 8 a of the conductive paste 8 arefilled with the resin film 1 to the height of Also, the conductive pastefillers 8 of the respective multilayer wiring board assembly components20 a to 20 c are fixedly pressed and finally cured by thermocompressionat the same time. By this configuration, the multilayer wiring boardassembly components 20 a to 20 c are united together with the copperfoil 9.

As explained in the above, in accordance with this embodiment asdescribed above, since the through holes 7 of the multilayer wiringboard assembly component 20 a to 20 c are filled with the conductivepaste fillers 8, it is possible to make the interlayer interconnectionbetween each adjacent layers by via-on-via. Also, since the projection 8b of the conductive paste filler 8 is formed in the rare surface opposedto the printing surface, it is possible to make the printing surface ofthe conductive paste filler 8 to be in close contact with the projection8 a when the interlayer interconnection is made by via-on-via andtherefore it becomes easy to make the electric connection between theconductive paste fillers 8 having good electric connectivity.

Also, since the conductive paste filler 8 is embedded in the throughhole 7 during printing operation in order that the printing surfacethereof is laterally extended from the opening 5 of the copper foil 2,the brim 8 a of the conductive paste filler 8 makes reliable electriccontact with the inner side surface and the upper surface of the copperfoil 2 beyond the perimeter of the opening 5 thereof, and therefore itis possible to connect the copper foil 2 to the conductive paste filler8 without compromising the electric connectivity between the fillers ofthe conductive paste.

Furthermore, since the copper plated resin film 10 is used in themanufacturing process of the multilayer wiring board assembly component,it becomes easy to preserve the accuracy of alignment of dimensions andpositions when holding a sample, opening a hole and filling the holeand, as a result, it is possible to save labor in the manufacturingworks. Namely, in the case of a conventional case, the respective stepsof holding a sample, opening a hole and filling the hole have to beconducted with a resin film (the polyimide film) having a smallthickness as it is. However, in accordance with this embodiment, therespective steps of holding a sample, opening a hole and filling thehole are conducted after bonding the copper foil 2 to the resin film 1and therefore it becomes easy to open and fill holes with the conductivepaste fillers 8.

FIG. 4 to FIG. 6 are cross sectional views showing the connectionterminal structure of a multilayer wiring board assembly in accordancewith the present invention on which an IC chip is mounted or which isused as an interposer.

In FIG. 4, by electroless gold plating with the multilayer wiring boardassembly 30 as illustrated in (a) of the same figure, a plating layer 11is formed on the external exposed surfaces of the conductive pastefiller 8 and the copper foil 9 as illustrated in (b) of the same figure,followed by further forming a solder bump 12 thereon in (c) of the samefigure. Meanwhile, any other type of plating technique available thangold plating for plating solder can be used for this purpose such asnickel-gold plating.

In FIG. 5, a bump 13 is formed by printing the conductive paste on topof the external exposed portion of the conductive paste filler 8 of themultilayer wiring board assembly 30 as illustrated in (a) of the samefigure.

In FIG. 6, as illustrated in (b) of the same figure, an anisotropicconductive film 16 is attached to at least the vicinity of theconnection terminal of the external exposed portion of the conductivepaste filler 8 of the multilayer wiring board assembly 30 as illustratedin (a) of the same figure.

In this manner, since it is possible to provide an FPC in the form of ahigh density and flexible multilayered structure in accordance with thepresent invention, the size of an electronic appliance can be reduced bymaking use of the FPC according to the multilayer wiring board assemblywhile an electronic appliance having a curved profile can be providedwith additional functionality, for example, by implementing a printedcircuit board in a watch strap with high density circuits.

Next, with reference to FIG. 7, FIG. 8, FIG. 9 and FIG. 10, a multilayerwiring board assembly component and the multilayer wiring board assemblyin accordance with a further embodiment of the present invention will beexplained.

In the case of this embodiment, a multilayer wiring board assembly islaminated by the use of first and second multilayer wiring boardassembly components. The first multilayer wiring board assemblycomponent is formed by making use of a screen printing technique inorder that a through hole is filled with a conductive paste filler whichis laterally extending on the upper surface of the copper foil beyondthe perimeter of the opening of the through hole. On the other hand, ascreen printing technique is not used for forming the second multilayerwiring board assembly component in order that a through hole is filledwith a conductive paste filler of which surface is flush with thesurface of the copper foil. More specifically explained, the secondmultilayer wiring board assembly component as described above is used asthe most outer unit of the multilayer wiring board assembly while thefirst multilayer wiring board assembly component as described above isused as at least one of the inner layers.

Next, the first multilayer wiring board assembly component as describedabove will be explained with reference to FIG. 7.

The first multilayer wiring board assembly component 20 is a connectionunit for use in the process of laminating a multilayer wiring boardassembly and comprises an FPC as a base element made of a single sidedcopper plated resin film. Namely, as illustrated in FIG. 7(j), themultilayer wiring board assembly component 20 is composed of a copperplated resin film 10 composed of a resin film 1 having adhesivity andmade of a thermoplastic polyimide (TPI) and the like and provided with acopper foil 2 bonded to one surface thereof, and a conductive pastefiller 12 embedded in a through hole 7 (refer to FIG. 7(g)) passedthrough the resin film 10 to form an inner via hole. A predeterminedcircuit pattern is formed in the copper foil 2 by etching and the like.The conductive paste filler 12 is embedded in the through hole 7 fromthe surface of the copper foil 2 by screen printing and so forth andlaterally extending on the upper surface of the copper foil 2 as a brim12 a beyond the perimeter of the opening thereof with the printingsurface of the conductive paste filler 12 being flat and flush therewithin order that the leading end thereof is projected as a projection 12 bthrough the opposed surface of the copper plated resin film 10 havingthe resin film 1.

While the resin film 1 is made of a material which is flexible, i.e.,bendable in the case of the above described embodiment, the resin film 1can be made of a rigid material such as a glass epoxy prepreg, anaramid-epoxy prepreg.

Also, a BT resin, a PPO, a PPE and the like can be used as the materialfor forming the above described resin film 1.

The multilayer wiring board assembly is laminated by stacking, as innerlayers, a plurality of the first multilayer wiring board assemblycomponents as illustrated in FIG. 7(j) (if the respective layers arecalled as first, second and third layers from the upper outer layer inthe case of the embodiment as illustrated in FIG. 9 and FIG. 10, thesecond and third layers are prepared in the form of the first multilayerwiring board assembly component). As illustrated in FIG. 9 and FIG. 10,since the through hole 7 of the multilayer wiring board assemblycomponent is filled with the conductive paste fillers 12 and 14, it ispossible to make interlayer connection via-on-via.

In this manner, when the interlayer interconnection is made byvia-on-via, the conductive paste fillers 12 are connected directly toeach other rather than through an intervening copper foil therebetween.

Next, the manufacturing process of the first multilayer wiring boardassembly component as described above will be explained with referenceto FIG. 7.

At first, as illustrated in FIG. 7(a), a single sided copper platedresin film 10 is provided or prepared as the resin film 1 made of athermoplastic polyimide film having a thickness of 30 to 100 micrometerwith the copper foil 2 having a thickness of 5 to 18 micrometer bondedto one surface.

Next, as illustrated in FIG. 7(b), a dry film (resist) 4 is laminated tothe copper foil 2 bonded to the resin film 1 with a vacuum laminator ora roll laminator. Next, as illustrated in FIG. 7(c), the dry film 4 isexposed to radiation of a circuit pattern followed by developing the dryfilm 4.

Next, as illustrated in FIG. 7(d), a predetermined circuit pattern isformed by etching the copper foil 2 with the dry film 4 as a mask. Inthis step, the opening 5 is formed by the same etching process for usein the subsequent step of opening the through hole 7. Next, after thedry film 4 is removed from the copper foil 2 as illustrated in FIG.7(e), a masking tape 6 having a thickness of 10 to 50 micrometer isbonded as a mask to the surface of the resin film 1 as illustrated inFIG. 7(f). The masking tape 6 may be made of a PET and the like.

Next, as illustrated in FIG. 7(g), the through hole 7 of 0.05 to 0.3 mmdiameter is opened in the resin film 1 through the resin film 1 and themasking tape 6 by exposing them to a laser light the opening 5 by meansof a CO₂ laser and the like. Meanwhile, the through hole 7 may be openedby means of a drill in place of the laser exposure process.

In this case, since the through hole 7 is formed through the opening 5by means of a CO₂ laser, it is possible to open a smaller hole (50 to250 micrometer diameter). Namely, if the through hole 7 were formedthrough the copper foil 2 in which the opening 5 had not be formed inadvance, a CO₂ laser (capable of opening holes of 50 to 250 micrometerdiameter) is not used for this purpose and therefore a larger hole of200 micrometer diameter or larger has to be opened by means of a drill(capable of opening holes of 200 micrometer diameter or larger).Meanwhile, some other lasers such as a UV-YAG laser, an excimer lasermay be used for this purpose of opening small holes. However, theselasers is too expensive to use for this purpose and therefore notpractical.

Meanwhile, since the through hole 7 as described above is passed alsothrough the copper foil 2, there are not generated voids, smear, as wellas the like drawbacks, which are likely if the conductive paste filler12 is embedded with the copper foil 2 as it is.

Next, as illustrated in FIGS. 7(h) and (i), the conductive paste 12 isplaced on the copper foil 2 and the mask 33 and spread to fill thethrough hole 7 therewith by moving a squeezee 32 made of an urethane,silicone and the like in the direction of arrow A. At this time, abreathable separate paper 31 as siliconized or fluoridized is placed forthe purpose of preserving the conductive paste 12 at the leading end ofthe through hole 7 near the resin film 1.

In this case, the separate paper 31 is provided with breathability forthe purpose of enabling air to escape when the through hole 7 is filledwith the conductive paste 12. Also, at least the upper surface of theseparate paper 31 is siliconized or fluoridized as described above forthe purpose of making easy to remove the separate paper 31 from theconductive paste filler 12 in contact with the separate paper 31 andpreventing the conductive paste filler 12 from being detached from thethrough hole 7 when the separate paper 31 is removed.

At this time, the conductive paste filler 12 is screen printed with adiameter larger than the opening 5 (the through hole 7) by about 10% to50% so that part of the conductive paste remains on the upper surface ofthe copper foil 2 beyond the perimeter of the opening 5 thereof. By thisconfiguration, there is formed the brim 12 a which is connected to theland surface 2 a of the copper foil 2 in the direction normal to thesurface. In this case, however, the printing surface of the conductivepaste filler 12 is made flat.

Meanwhile, Ag, Cu, C, Cu coated with Ag and other conductive pastes canbe used to form the conductive paste filler 12.

Next, after removing the separate paper 31, the projection 12 b of theconductive paste filler 12 which is projecting through the resin film 1in the surface opposed to the printing surface is formed by heating theconductive paste filler 12 in an oven at 80° C. for an hour to partiallycure the conductive paste filler 12 and removing the masking tape 6 asillustrated in FIG. 7(j). By this process, the first multilayer wiringboard assembly component 20 is completely formed.

Next, the second multilayer wiring board assembly component as describedabove will be explained with reference to FIG. 8.

The second multilayer wiring board assembly component 20′ is aconnection unit for use in the process of laminating a multilayer wiringboard assembly and comprises an FPC as a base element made of a singlesided copper plated resin film. Namely, as illustrated in FIG. 8(j), themultilayer wiring board assembly component 20 is composed of a copperplated resin film 10 composed of a resin film 1 having adhesivity andmade of a thermoplastic polyimide (TPI) and the like and provided with acopper foil 2 bonded to one surface thereof, and a conductive pastefiller 12 embedded in a through hole 7 (refer to FIG. 8(g)) passedthrough the resin film 10 to form an inner via hole. A predeterminedcircuit pattern is formed in the copper foil 2 by etching and the like.The conductive paste filler 14 is embedded in the through hole 7 fromthe surface of the copper foil 2 a by printing with the printing surface14 c of the conductive paste filler 14 being flat and flush with theupper surface 2 c of the copper foil 2 a in order that the leading endthereof is projected as a projection 14 b through the opposed surface ofthe copper plated resin film 10 having the resin film 1. Namely, asillustrated in FIG. 8(j), the upper surface 2 c of the copper foil 2 aand the printing surface 14 c of the conductive paste filler 14 areconnected to form a continuous flat surface having the same height.

While the resin film 1 is made of a material which is flexible, i.e.,bendable in the case of the above described embodiment, the resin film 1can be made of a rigid material such as a glass epoxy prepreg, anaramid-epoxy prepreg.

Also, a BT resin, a PPO, a PPE and the like can be used as the materialfor forming the above described resin film 1.

The multilayer wiring board assembly is laminated by stacking, as anouter layer, the second multilayer wiring board assembly component asillustrated in FIG. 8(j) (if the respective layers are called as first,second and third layers from the upper outer layer in the case of theembodiment as illustrated in FIG. 10 and FIG. 11, the second multilayerwiring board assembly component is the first layer). As illustrated inFIG. 10 and FIG. 11, since the through hole 7 of the multilayer wiringboard assembly component is filled with the conductive paste fillers 12and 14, it is possible to make interlayer connection via-on-via.

Next, the manufacturing process of the second multilayer wiring boardassembly component as described above will be explained with referenceto FIG. 8.

At first, as illustrated in FIG. 8(a), a single sided copper platedresin film 10 is provided or prepared as the resin film 1 made of athermoplastic polyimide film having a thickness of 30 to 100 micrometerwith the copper foil 2 having a thickness of 5 to 18 micrometer bondedto one surface.

Next, as illustrated in FIG. 8(b), a dry film (resist) 4 is laminated tothe copper foil 2 bonded to the resin film 1 with a vacuum laminator ora roll laminator. Next, as illustrated in FIG. 8(c), the dry film 4 isexposed to radiation of a pattern of the opening of the through hole 7,followed by developing the dry film 4. In the case, the dry film 4 a isdeveloped in order to be continuous except for the opening 5.

Next, as illustrated in FIG. 8(d), the copper foil 2 is etched with thedry film 4 a as a mask to form the copper foil 2 a having thepredetermined opening 5. In this step, the opening 5 is formed by thesame etching process for use in the subsequent step of opening thethrough hole 7. By this configuration, as illustrated in FIG. 9(a), thecopper foil 2 a is formed in a continuous fashion in the locations otherthan the conductive paste 14.

Next, after the dry film 4 a is removed from the copper foil 2 a asillustrated in FIG. 8(e), a masking tape 6 having a thickness of 10 to50 micrometer is bonded as a mask to the surface of the resin film 1 asillustrated in FIG. 8(f). The masking tape 6 may be made of a PET andthe like.

Next, as illustrated in FIG. 8(g), the through hole 7 of 0.05 to 0.3 mmdiameter is opened in the resin film 1 through the resin film 1 and themasking tape 6 by exposing them to a laser light through the opening 5by means of a CO₂ laser and the like.

Since the through hole 7 is opened after forming the opening 5, it ispossible to form a small hole as described above.

Meanwhile, since the through hole 7 as described above is passed alsothrough the copper foil 2, there are not generated voids, smear, as wellas the like drawbacks, which are likely if the conductive paste filler12 is embedded with the copper foil 2 as it is.

Next, as illustrated in FIGS. 8(h) and (i), the conductive paste 14 isplaced on the copper foil 2 and spread to fill the through hole 7therewith by moving a squeezee 32 made of an urethane, silicone and thelike in the direction of arrow A. At this time, a breathable separatepaper 31 as siliconized or fluoridized is placed for the purpose ofpreserving the conductive paste 14 at the leading end of the throughhole 7 near the resin film 1.

In this case, the separate paper 31 is provided with breathability forthe purpose of enabling air to escape when the through hole 7 is filledwith the conductive paste 14. Also, at least the upper surface of theseparate paper 31 is siliconized or fluoridized as described above forthe purpose of making easy to remove the separate paper 31 from theconductive paste filler 14 in contact with the separate paper 31 andpreventing the conductive paste filler 14 from being detached from thethrough hole 7 when the separate paper 31 is removed.

In this case, as illustrated in FIG. 8(j), the upper surface 2 c of thecopper foil 2 a and the printing surface 14 c of the conductive pastefiller 14 are connected to form a continuous flat surface having thesame height.

Meanwhile, Ag, Cu, C, Cu coated with Ag and other conductive pastes canbe used to form the conductive paste filler 14.

Next, after removing the separate paper 31, the projection 14 b of theconductive paste filler 14 which is projecting through the resin film 1in the surface opposed to the printing surface is formed by heating theconductive paste filler 14 in an oven at 80° C. for an hour to partiallycure the conductive paste filler 14 and removing the masking tape 6 asillustrated in FIG. 8(i). By this process, the second multilayer wiringboard assembly component 20′ is completely formed.

FIG. 9 shows a modification of the manufacturing process of themultilayer wiring board assembly component 20′ as described above.

In this modification, while the opening 5 is not formed in the copperfoil 2, the through hole 7 is opened also in the copper foil 2. By thisconfiguration, the step of forming the opening 5 is dispensed with sothat it is possible to decrease the number of the manufacturing steps.

Namely, as illustrated in FIG. 9(a), a single sided copper plated resinfilm 10 is provided or prepared as the resin film 1 made of athermoplastic polyimide film having a thickness of 30 to 100 micrometerwith the copper foil 2 having a thickness of 5 to 18 micrometer bondedto one surface.

Next, as illustrated in FIG. 9(b), the through hole 7 of 0.2 mm diameteris opened in the copper foil 2 and the masking tape 6 through the resinfilm 1.

Next, as illustrated in FIGS. 9(c) and (d), the conductive paste 14 isplaced on the copper foil 2 and spread to fill the through hole 7therewith by moving a squeezee 32 made of an urethane, silicone and thelike in the direction of arrow A. At this time, a breathable separatepaper 31 as siliconized or fluoridized is placed for the purpose ofpreserving the conductive paste 14 at the leading end of the throughhole 7 near the resin film 1.

In this case, the separate paper 31 is provided with breathability forthe purpose of enabling air to escape when the through hole 7 is filledwith the conductive paste 14. Also, at least the upper surface of theseparate paper 31 is siliconized or fluoridized as described above forthe purpose of making easy to remove the separate paper 31 from theconductive paste filler 14 in contact with the separate paper 31 andpreventing the conductive paste filler 14 from being detached from thethrough hole 7 when the separate paper 31 is removed.

Meanwhile, Ag, Cu, C, Cu coated with Ag and other conductive pastes canbe used to form the conductive paste filler 14.

Next, after removing the separate paper 31, the projection 14 b of theconductive paste filler 14 which is projecting through the resin film 1in the surface opposed to the printing surface is formed by heating theconductive paste filler 14 in an oven at 80° C. for an hour to partiallycure the conductive paste filler 14 and removing the masking tape 6 asillustrated in FIG. 9(e). By this process, the second multilayer wiringboard assembly component 20′ is completely formed.

Next, the press step for manufacturing a multilayer wiring boardassembly by joining the first and second multilayer wiring boardassembly components 20 and 20′ together will be explained with referenceto FIG. 10 and FIG. 11.

As illustrated in FIG. 10, the multilayer wiring board assembly iscomposed of the second multilayer wiring board assembly component 20′ asillustrated in FIG. 8(j) or FIG. 9(e) arranged as a most outer layer(most upper layer) and the first multilayer wiring board assemblycomponent 20 as illustrated in FIG. 7(j) arranged as the other layers(inner layers) which are laminated with the second multilayer wiringboard assembly component 20′. The respective layers are formed with aplurality of circuit patterns and through holes 7 which are filled withthe conductive paste fillers 12 and 14.

The formation of the multilayer wiring board assembly in accordance withthe present embodiment is completed by laminating together, at a time orsuccessively, the respective first and second multilayer wiring boardassembly components 20 a to 20 c by thermocompression with a most outercopper foil 9 as illustrated in FIG. 11(a) and forming a circuit on themost outer copper foil 9.

In this case, as illustrated in FIG. 11(a), the upper surface of themost outer layer (most upper layer) is formed in order that the uppersurface 2 c of the copper foil 22 a and the leading end of theconductive paste filler 14, i.e., the printing surface 14 c, arearranged to form a continuous flat surface having the same height sothat it is possible to apply a uniform pressure to the entirety of themultilayer wiring board assembly during thermocompression. By thisconfiguration, the multilayer wiring board assembly is fixedly laminatedwith a better electric connectivity.

The step of laminating the respective multilayer wiring board assemblycomponents 20 and 20′ and the most outer copper foil 9 to each other bythermocompression is carried out by heating them at 280° C. orthereabout and pressing them at 9 MPa or thereabout in order to embedthe circuit pattern of the copper foil 2 and the brim 12 a of theconductive paste filler 12 in the resin film 1 made of a thermoplasticpolyimide having adhesivity and fluidity. At this time, the conductivepaste fillers 12 and 14 of the respective multilayer wiring boardassembly components 20 and 20′ are fixedly pressed and finally cured bythermocompression at the same time.

Finally, as illustrated in FIG. 11(b), a circuit pattern is formed inthe most outer copper foil 2 a by etching and the like followed byplating the copper foil 2 a with a metallic layer 15 for the purpose ofincreasing the area available for electric contact with the conductivepaste filler 14. While the metallic layer 15 may be formed of anyconductive material such as Au, Ni, Hg, Ag, Rh and Pd, the use of Au isparticularly preferable in consideration of oxidation-proof andfacilitating bonding.

In accordance with this embodiment as described above, since the throughholes 7 of the first and second multilayer wiring board assemblycomponent 20 and 20′ are filled with the conductive paste fillers 12 and14, it is possible to make the interlayer interconnection between eachadjacent layers by via-on-via. Also, since the projections 12 b and 14 bof the conductive paste fillers 12 and 14 is formed, it becomes easy tomake the electric connection between the conductive paste fillers 12 and14 having good electric connectivity when the interlayer interconnectionis made by via-on-via.

Also, since the conductive paste filler 12 of the first multilayerwiring board assembly component 20 is embedded in the through hole 7during printing operation in order that the printing surface thereof islaterally extended from the opening 5 of the copper foil 2, the brim 12a of the conductive paste filler 12 makes reliable electric contact withthe inner side surface and the upper surface of the copper foil 2 beyondthe perimeter of the opening 5 thereof, and therefore it is possible toconnect the copper foil 2 to the conductive paste filler 12 withoutcompromising the electric connectivity between the copper foil 2 and thefillers of the conductive paste.

Furthermore, since the copper plated resin film 10 is used in themanufacturing process of the multilayer wiring board assembly component,it becomes easy to preserve the accuracy of alignment of dimensions andpositions when holding a sample, opening a hole and filling the holeand, as a result, it is possible to save labor in the manufacturingworks. Namely, in the case of a conventional case, the respective stepsof holding a sample, opening a hole and filling the hole have to beconducted with a resin film (the polyimide film) having a smallthickness as it is. However, in accordance with this embodiment, therespective steps of holding a sample, opening a hole and filling thehole are conducted after bonding the copper foil 2 to the resin film 1and therefore it becomes easy to open and fill holes with the conductivepaste fillers 12.

Furthermore, since a desired multilayer wiring board assembly can beformed only by preparing multilayer wiring board assembly components asdescribed above and combining and joining them together, the press stepfor a multilayer wiring board assembly becomes easy without need forconducting press steps of multilayer wiring board assembly components.

As described above, the upper surface of the most outer layer (mostupper layer) is formed in order that the upper surface of the copperfoil and the leading end of the conductive paste filler, i.e., theprinting surface, are arranged to form a continuous flat surface havingthe same height so that it is possible to apply a uniform pressure tothe entirety of the multilayer wiring board assembly duringthermocompression. By this configuration, the multilayer wiring boardassembly is fixedly laminated with a better electric connectivity.

Next, with reference to FIG. 12, FIG. 13 and FIG. 14, a multilayerwiring board assembly component and the multilayer wiring board assemblyin accordance with a further embodiment of the present invention will beexplained.

In the case of this embodiment, a multilayer wiring board assembly islaminated by the use of a plurality of multilayer wiring board assemblycomponents, each of which is prepared by embedding a conductive paste ina through hole by screen printing with a mask in order that theconductive paste filler is laterally extending beyond the perimeter ofthe opening of the through hole.

Next, the above described multilayer wiring board assembly componentwill be explained with reference to FIG. 12.

The multilayer wiring board assembly component 20 is a connection unitfor use in the process of laminating a multilayer wiring board assemblyand comprises an FPC as a base element made of a single sided copperplated resin film. Namely, as illustrated in FIG. 12(j), the multilayerwiring board assembly component 20 is composed of a copper plated resinfilm 10 composed of a resin film 1 having adhesivity and made of athermoplastic polyimide (TPI) and the like and provided with a copperfoil 2 bonded to one surface thereof, and a conductive paste filler 12embedded in a through hole 7 (refer to FIG. 12(g)) passed through theresin film 10 to form an inner via hole. A predetermined circuit patternis formed in the copper foil 2 by etching and the like. The conductivepaste filler 12 is embedded in the through hole 7 from the surface ofthe copper foil 2 by screen printing and so forth with a mask and islaterally extending on the upper surface of the copper foil 2 as a brim12 a beyond the perimeter of the opening thereof with the printingsurface 12 c of the conductive paste filler 12 being flat and flushtherewith in order that the leading end thereof is projected as aprojection 12 b through the opposed surface of the copper plated resinfilm 10 having the resin film 1.

While the resin film 1 is made of a material which is flexible, i.e.,bendable in the case of the above described embodiment, the resin film 1can be made of a rigid material such as a glass epoxy prepreg, anaramid-epoxy prepreg.

Also, a BT resin, a PPO, a PPE and the like can be used as the materialfor forming the above described resin film 1.

A multilayer wiring board assembly is laminated by stacking a pluralityof the multilayer wiring board assembly components as illustrated inFIG. 12(i) (three units in the case of the embodiment as illustrated inFIG. 13 and FIG. 14). As illustrated in FIG. 13 and FIG. 14, since thethrough hole 7 of the multilayer wiring board assembly component isfilled with the conductive paste filler 12, it is possible to makeinterlayer connection via-on-via.

In this manner, when the interlayer interconnection is made byvia-on-via, the conductive paste fillers 12 are connected directly toeach other rather than through an intervening copper foil therebetween.

Next, the manufacturing process (method) of the multilayer wiring boardassembly in accordance with the present invention will be explained withreference to FIG. 12.

At first, as illustrated in FIG. 12(a), a single sided copper platedresin film 10 is provided or prepared as the resin film 1 made of athermoplastic polyimide film having a thickness of 15 to 100 micrometerwith the copper foil 2 having a thickness of 5 to 18 micrometer bondedto one surface.

Next, as illustrated in FIG. 12(b), a dry film (resist) 4 is laminatedto the copper foil 2 bonded to the resin film 1 with a vacuum laminatoror a roll laminator. Next, as illustrated in FIG. 12(c), the dry film 4is exposed to radiation of a circuit pattern followed by developing thedry film 4.

Next, as illustrated in FIG. 12(d), a predetermined circuit pattern isformed by etching the copper foil 2 with the dry film 4 as a mask. Inthis step, the opening 5 is formed by the same etching process for usein the subsequent step of opening the through hole 7. Next, after thedry film 4 is removed from the copper foil 2 as illustrated in FIG.12(e), a masking tape 6 having a thickness of 10 to 50 micrometer isbonded as a mask to the surface of the resin film 1 as illustrated inFIG. 12(f). The masking tape 6 may be made of a PET and the like.

Next, as illustrated in FIG. 12(g), the through hole 7 of 0.05 to 0.3 mmdiameter is opened in the resin film 1 through the resin film 1 and themasking tape 6 by exposing them to a laser light through the opening 5by means of a CO₂ laser and the like. Meanwhile, the through hole 7 maybe opened by means of a drill in place of the laser exposure process.

In this case, since the through hole 7 is formed through the opening 5by means of a CO₂ laser, it is possible to open a smaller hole (50 to250 micrometer diameter). Namely, if the through hole 7 were formedthrough the copper foil 2 in which the opening 5 had not be formed inadvance, a CO₂ laser (capable of opening holes of 50 to 250 micrometerdiameter) is not used for this purpose and therefore a larger hole of200 micrometer diameter or larger has to be opened by means of a drill(capable of opening holes of 200 micrometer diameter or larger).Meanwhile, some other lasers such as a UV-YAG laser, an excimer lasermay be used for this purpose of opening small holes. However, theselasers is too expensive to use for this purpose and therefore notpractical.

Meanwhile, since the through hole 7 as described above is passed alsothrough the copper foil 2, there are not generated voids, smear, as wellas the like drawbacks, which are likely if the conductive paste filler12 is embedded with the copper foil 2 as it is.

Next, a conductive paste is screen printed to fill the through hole 7with the conductive paste filler 12. In this case, as illustrated inFIG. 12(h), an amount of the conductive paste 12 is placed on the copperfoil 2 and spread to fill the through hole 7 therewith by moving asqueezee 32 made of an urethane, silicone and the like in the directionof arrow A, after a metallic mask (or a screen mask) 33 having a hole ofa diameter larger than that of the through hole 7 is placed on thecopper foil 2 in order that part of the conductive paste remains on theupper surface of the copper foil 2 beyond the perimeter of the opening5, and after a breathable separate paper 31 as siliconized orfluoridized is placed for the purpose of preserving the conductive paste12 at the leading end of the through hole 7 near the masking tape 6.

In this case, the separate paper 31 is provided with breathability forthe purpose of enabling air to escape when the through hole 7 is filledwith the conductive paste 12. Also, at least the upper surface of theseparate paper 31 is siliconized or fluoridized as described above forthe purpose of making easy to remove the separate paper 31 from theconductive paste filler 12 in contact with the separate paper 31 andpreventing the conductive paste filler 12 from being detached from thethrough hole 7 when the separate paper 31 is removed.

By this configuration, as illustrated in FIG. 12(i), after removing themetallic mask 33 and the separate paper 31, the conductive paste filler12 is screen printed with a diameter larger than the opening 5 (thethrough hole 7) by about 10% to 50% so that part of the conductive pasteremains on the upper surface of the copper foil 2 beyond the perimeterof the opening 5 thereof. By this configuration, there is formed thebrim 12 a which is connected to the land surface 2 a of the copper foil2 in the direction normal to the surface. In this case, however, theprinting surface 12 c of the conductive paste filler 12 is made flat.

Meanwhile, Ag, Cu, C, Cu coated with Ag and other conductive pastes canbe used to form the conductive paste filler 12.

Also, while the conductive paste filler 12 is formed by screen printingas described above, another suitable printing technique is used for thispurpose.

Next, the projection 12 b of the conductive paste filler 12 which isprojecting through the resin film 1 in the surface opposed to theprinting surface is formed by heating the conductive paste filler 12 inan oven at 80° C. to partially cure the conductive paste filler 12 andremoving the masking tape 6 as illustrated in FIG. 12(j). By thisprocess, the multilayer wiring board assembly component 20 is completelyformed.

Next, the press step for manufacturing a multilayer wiring boardassembly by joining a plurality of the multilayer wiring board assemblycomponents 20 as described above will be explained with reference toFIG. 13 and FIG. 14.

As illustrated in FIG. 13, a plurality of circuit patterns and aplurality of through holes 7 are formed on each of the multilayer wiringboard assembly components (three multilayer wiring board assemblycomponents) 20 a, 20 b and 20 c. Also, the through holes 7 are filledwith the conductive paste fillers 12.

The formation of the multilayer wiring board assembly in accordance withthe present embodiment is completed by laminating together therespective multilayer wiring board assembly components 20 a to 20 c bythermocompression with a most outer copper foil 9 at the same time orsequentially as illustrated in FIG. 14(a) and forming a circuit on themost outer copper foil 9 as illustrated in FIG. 14(b). The step oflaminating the respective multilayer wiring board assembly components 20a to 20 c and the most outer copper foil 9 to each other bythermocompression is carried out by heating them at 280° C. orthereabout and pressing them at 9 MPa or thereabout in order to embedthe circuit pattern of the copper foil 2 and the brim 12 a of theconductive paste filler 12 in the resin film 1 made of a thermoplasticpolyimide having adhesivity and fluidity. At this time, the conductivepaste fillers 12 of the respective multilayer wiring board assemblycomponents 20 a to 20 c are fixedly pressed and finally cured bythermocompression at the same time.

In accordance with this embodiment as described above, since the throughholes 7 of the multilayer wiring board assembly component 20 a to 20 care filled with the conductive paste fillers 12, it is possible to makethe interlayer interconnection between each adjacent layers byvia-on-via. Also, since the projection 12 b of the conductive pastefiller 12 is formed in the printing surface, it becomes easy to make theelectric connection between the conductive paste fillers 12 having goodelectric connectivity when the interlayer interconnection is made byvia-on-via.

Also, since the conductive paste filler 12 is embedded in the throughhole 7 during printing operation in order that the printing surfacethereof is laterally extended from the opening 5 of the copper foil 2,the brim 12 a of the conductive paste filler 12 makes reliable electriccontact with the inner side surface and the upper surface of the copperfoil 2 beyond the perimeter of the opening 5 thereof, and therefore itis possible to connect the copper foil 2 to the conductive paste filler12 without compromising the electric connectivity between the copperfoil 2 and the fillers of the conductive paste.

Furthermore, since the copper plated resin film 10 is used in themanufacturing process of the multilayer wiring board assembly component,it becomes easy to preserve the accuracy of alignment of dimensions andpositions when holding a sample, opening a hole and filling the holeand, as a result, it is possible to save labor in the manufacturingworks. Namely, in the case of a conventional case, the respective stepsof holding a sample, opening a hole and filling the hole have to beconducted with a resin film 1 (the polyimide film) having a smallthickness as it is. However, in accordance with this embodiment, therespective steps of holding a sample, opening a hole and filling thehole are conducted after bonding the copper foil 2 to the resin film 1and therefore it becomes easy to open and fill holes with the conductivepaste fillers 12.

Furthermore, since a desired multilayer wiring board assembly can beformed only by preparing multilayer wiring board assembly components asdescribed above and combining and joining them together, the press stepof a multilayer wiring board assembly becomes easy without need forconducting press steps of multilayer wiring board assembly components.

Next, with reference to FIG. 15, FIG. 16 and FIG. 17, a multilayerwiring board assembly component and the multilayer wiring board assemblyin accordance with a still further embodiment of the present inventionwill be explained.

In the case of this embodiment, a multilayer wiring board assembly islaminated by the use of a plurality of multilayer wiring board assemblycomponents, each of which is prepared by embedding a conductive paste ina through hole by the use of a plane table having a hole of a diameterlarger than that of the through hole in order that the conductive pastefiller is laterally extending beyond the perimeter of the opening of thethrough hole.

Next, the above described multilayer wiring board assembly componentwill be explained with reference to FIG. 15.

The multilayer wiring board assembly component 20 is a connection unitfor use in the process of laminating a multilayer wiring board assemblyand comprises an FPC as a base element made of a single sided copperplated resin film. Namely, as illustrated in FIG. 15(k), the multilayerwiring board assembly component 20 is composed of a copper plated resinfilm 10 composed of a resin film 1 having adhesivity and made of athermoplastic polyimide (TPI) and the like and provided with a copperfoil 2 bonded to one surface thereof, and a conductive paste filler 12embedded in a through hole 7 (refer to FIG. 15(g)) passed through theresin film 10 to form an inner via hole. A predetermined circuit patternis formed in the copper foil 2 by etching and the like. The conductivepaste filler 12 is embedded in the through hole 7 from the masking tape6 with the plane table 34 as explained in the following description byscreen printing and so forth and laterally extending on the uppersurface of the copper foil 2 as a brim 12 a beyond the perimeter of theopening thereof with the printing surface 12 c of the conductive pastefiller 12 being flat and flush therewith in order that the leading endthereof is projected as a projection 12 b through the opposed surface ofthe copper plated resin film 10 having the resin film 1.

While the resin film 1 is made of a material which is flexible, i.e.,bendable in the case of the above described embodiment, the resin film 1can be made of a rigid material such as a glass epoxy prepreg, anaramid-epoxy prepreg.

Also, a BT resin, a PPO, a PPE and the like can be used as the materialfor forming the above described resin film 1.

The multilayer wiring board assembly is laminated by stacking aplurality of the first multilayer wiring board assembly components asillustrated in FIG. 15(k) (three units in the case of the embodiment asillustrated in FIG. 16 and FIG. 17). As illustrated in FIG. 16 and FIG.17, since the through hole 7 of the multilayer wiring board assemblycomponent is filled with the conductive paste filler 12, it is possibleto make interlayer connection via-on-via.

In this manner, when the interlayer interconnection is made byvia-on-via, the conductive paste fillers 12 are connected directly toeach other rather than through an intervening copper foil therebetween.

Next, the manufacturing process (method) of the multilayer wiring boardassembly in accordance with the present invention will be explained withreference to FIG. 15.

At first, as illustrated in FIG. 15(a), a single sided copper platedresin film 10 is provided or prepared as the resin film 1 made of athermoplastic polyimide film having a thickness of 15 to 100 micrometerwith the copper foil 2 having a thickness of 5 to 18 micrometer bondedto one surface.

Next, as illustrated in FIG. 15(b), a dry film (resist) 4 is laminatedto the copper foil 2 bonded to the resin film 1 with a vacuum laminatoror a roll laminator. Next, as illustrated in FIG. 15(c), the dry film 4is exposed to radiation of a circuit pattern followed by developing thedry film 4.

Next, as illustrated in FIG. 15(d), a predetermined circuit pattern isformed by etching the copper foil 2 with the dry film 4 as a mask. Inthis step, the opening 5 is formed by the same etching process for usein the subsequent step of opening the through hole 7. Next, after thedry film 4 is removed from the copper foil 2 as illustrated in FIG.15(e), a masking tape 6 having a thickness of 10 to 50 micrometer isbonded as a mask to the surface of the resin film 1 as illustrated inFIG. 15(f). The masking tape 6 may be made of a PET and the like.

Next, as illustrated in FIG. 15(g), the through hole 7 of 0.05 to 0.3 mmdiameter is opened in the resin film 1 through the resin film 1 and themasking tape 6 by exposing them to a laser light through the opening 5by means of a CO₂ laser and the like. Meanwhile, the through hole 7 maybe opened by means of a drill in place of the laser exposure process.

In this case, since the through hole 7 is formed through the opening 5by means of a CO₂ laser, it is possible to open a smaller hole (50 to250 micrometer diameter). Namely, if the through hole 7 were formedthrough the copper foil 2 in which the opening 5 had not be formed inadvance, a CO₂ laser (capable of opening holes of 50 to 250 micrometerdiameter) is not used for this purpose and therefore a larger hole of200 micrometer diameter or larger has to be opened by means of a drill(capable of opening holes of 200 micrometer diameter or larger).Meanwhile, some other lasers such as a UV-YAG laser, an excimer lasermay be used for this purpose of opening small holes. However, theselasers is too expensive to use for this purpose and therefore notpractical.

Meanwhile, since the through hole 7 as described above is passed alsothrough the copper foil 2, there are not generated voids, smear, as wellas the like drawbacks, which are likely if the conductive paste filler12 is embedded with the copper foil 2 as it is.

Next, a conductive paste is screen printed to fill the through hole 7with the conductive paste filler 12. In this case, as illustrated inFIG. 15(h), an amount of the conductive paste 12 is spread to fill thethrough hole 7 therewith by moving a squeezee 32 made of an urethane,silicone and the like in the direction of arrow A, after preparing theplane table 34 having a hole 35 of a diameter larger than that of thethrough hole 7, placing the copper plated resin film 10 as illustratedin FIG. 15(g) on the hole 35 of the plane table 34 with the copper foil2 being positioned as the bottom of the multilayer wiring board assemblycomponent (i.e. it is inverted), and preselecting the coefficient ofviscosity of the conductive paste filler 12 and the printing conditionin order that part of the conductive paste remains on the upper surfaceof the copper foil 2 beyond the perimeter of the opening 5 of the copperfoil 2.

In this case, the coefficient of viscosity of the conductive paste 12 ispredetermined lower than that of the conductive paste 12 in the case ofthe embodiment as illustrated in FIG. 12. The profile of the conductivepaste filler 12 as described above is illustrated in FIG. 15(i). In thiscase, as illustrated in FIG. 15(i), the size of the hole 35 of the abovedescribed plane table 34 is predetermined to provide a sufficient spacein order that the conductive paste filler 12 is not so extending fromthe opening 5 of the copper foil 2 as to make contact with the planetable 34 after the filling step.

Next, when the lanimate is removed from the plane table 34 and inverted,the conductive paste is screen printed in order that the diameter of theconductive paste filler 12 is larger than the diameter of the opening 5(the through hole 7) by about 10% to 50% so that the conductive paste islaterally extending beyond the perimeter of the opening 5 thereof asillustrated in FIG. 15(i). By this configuration, there is formed thebrim 12 a which is connected to the land surface 2 a of the copper foil2 in the direction normal to the surface. In this case, however, theprinting surface 12 c of the conductive paste filler 12 is made flat. Itis therefore possible to form the brim 12 a of a smaller thickness witha higher degree of accuracy, as compared to the case utilizing a mask(refer to FIG. 12), by filling the through hole 7 with the conductivepaste filler 12 by the use of the plane table 34.

Meanwhile, Ag, Cu, C, Cu coated with Ag and other conductive pastes canbe used to form the conductive paste filler 12.

Also, while the conductive paste filler 12 is formed by screen printingas described above, another suitable printing technique is used for thispurpose.

Next, the projection 12 b of the conductive paste filler 12 which isprojecting through the resin film 1 in the surface opposed to theprinting surface is formed by heating the conductive paste filler 12 inan oven at 80° C. to partially cure the conductive paste filler 12 andremoving the masking tape 6 as illustrated in FIG. 15(k). By thisprocess, the multilayer wiring board assembly component 20 is completelyformed.

Next, the press step for manufacturing a multilayer wiring boardassembly by joining a plurality of the multilayer wiring board assemblycomponents 20 as described above will be explained with reference toFIG. 16 and FIG. 17.

As illustrated in FIG. 16, a plurality of circuit patterns and aplurality of through holes 7 are formed on each of the multilayer wiringboard assembly components (three multilayer wiring board assemblycomponents) 20 a, 20 b and 20 c. Also, the through holes 7 are filledwith the conductive paste fillers 12.

The formation of the multilayer wiring board assembly in accordance withthe present embodiment is completed by laminating together therespective multilayer wiring board assembly components 20 a to 20 c bythermocompression with a most outer copper foil 9 at the same time orsequentially as illustrated in FIG. 17(a) and forming a circuit on themost outer copper foil 9 as illustrated in FIG. 17(b). The step oflaminating the respective multilayer wiring board assembly components 20a to 20 c and the most outer copper foil 9 to each other bythermocompression is carried out by heating them at 280° C. orthereabout and pressing them at 9 MPa or thereabout in order to embedthe circuit pattern of the copper foil 2 and the brim 12 a of theconductive paste filler 12 in the resin film 1 made of a thermoplasticpolyimide having adhesivity and fluidity. At this time, the conductivepaste fillers 12 of the respective multilayer wiring board assemblycomponents 20 a to 20 c are fixedly pressed and finally cured bythermocompression at the same time.

In accordance with this embodiment as described above, since the throughholes 7 of the multilayer wiring board assembly component 20 a to 20 care filled with the conductive paste fillers 12, it is possible to makethe interlayer interconnection between each adjacent layers byvia-on-via. Also, since the projection 12 b of the conductive pastefiller 12 is formed in the printing surface, it becomes easy to make theelectric connection between the conductive paste fillers 12 having goodelectric connectivity when the interlayer interconnection is made byvia-on-via.

Also, since the conductive paste filler 12 is embedded in the throughhole 7 during printing operation in order that the printing surfacethereof is laterally extended from the opening 5 of the copper foil 2,the brim 12 a of the conductive paste filler 12 makes reliable electriccontact with the inner side surface and the upper surface of the copperfoil 2 beyond the perimeter of the opening 5 thereof, and therefore itis possible to connect the copper foil 2 to the conductive paste filler12 without compromising the electric connectivity between the copperfoil 2 and the fillers of the conductive paste.

Furthermore, since the copper plated resin film 10 is used in themanufacturing process of the multilayer wiring board assembly component,it becomes easy to preserve the accuracy of alignment of dimensions andpositions when holding a sample, opening a hole and filling the holeand, as a result, it is possible to save labor in the manufacturingworks. Namely, in the case of a conventional case, the respective stepsof holding a sample, opening a hole and filling the hole have to beconducted with a resin film 1 (the polyimide film) having a smallthickness as it is. However, in accordance with this embodiment, therespective steps of holding a sample, opening a hole and filling thehole are conducted after bonding the copper foil 2 to the resin film 1and therefore it becomes easy to open and fill holes with the conductivepaste fillers 12.

Furthermore, since a desired multilayer wiring board assembly can beformed only by preparing multilayer wiring board assembly components asdescribed above and combining and joining them together, the press stepof a multilayer wiring board assembly becomes easy without need forconducting press steps of multilayer wiring board assembly components.

Furthermore, in accordance with the present invention, the opening ofthe through hole near the copper foil is placed on the plane tablehaving a hole of a diameter larger than that of the through holefollowed by filling the through hole with the conductive paste from theleading end of the masking tape in order to form a brim laterallyextending beyond the perimeter of the opening of the copper foil, andtherefore it is possible to form the brim having a desired profile witha high degree of accuracy and having a smaller thickness than that inthe case utilzing a mask. By this configuration, the multilayer wiringboard assembly is fixedly laminated with a better electric connectivity.

Next, with reference to FIG. 18, FIG. 19 and FIG. 20, a multilayerwiring board assembly component and the multilayer wiring board assemblyin accordance with a still further embodiment of the present inventionwill be explained.

In the case of this embodiment, the multilayer wiring board assembly islaminated by laminating together a plurality of multilayer wiring boardassembly components, each of which is made by preparing a copper platedresin film made of a adhesive resin film which is provided with a copperfoil bonded to one surface thereof, attaching masking tapes to the bothsurfaces of the copper plated resin film, opening a through hole in thecopper plated resin film through the masking tape, filling the throughhole with a conductive paste to form a conductive paste filler havingend surfaces flush with the surfaces of the masking tape, removing themasking tape after the formation of the conductive paste filler to formprojections of the conductive paste filler in the both surfaces thereof.

Next, the above described multilayer wiring board assembly componentwill be explained with reference to FIG. 18. The multilayer wiring boardassembly component 20′ is a connection unit for use in the process oflaminating a multilayer wiring board assembly and comprises an FPC as abase element made of a single sided copper plated resin film. Namely, asillustrated in FIG. 18(j), the multilayer wiring board assemblycomponent 20 is composed of a copper plated resin film 10 composed of aresin film 1 having adhesivity and made of a thermoplastic polyimide(TPI) and the like and provided with a copper foil 2 bonded to onesurface thereof, and a conductive paste filler 12 embedded in a throughhole 7 (refer to FIG. 18(g)) passed through the resin film 10 to form aninner via hole. The conductive paste filler 14 is formed to have anleading end projecting from the upper surface 2 c of the copper foil 2as a projection 14 c and a tail end projecting from the lower surface ofthe resin film 1 as the projection 14 b. Namely, as illustrated in FIGS.18(h) through (j), the projections 14 c and 14 b are formed by removingthe masking tapes 6 a and 6 b as described above after embedding theconductive paste filler 14 from the copper foil 2 by printing and thelike in the through hole 7 of the copper plated resin film 10 with themasking tapes 6 a and 6 b on the both surfaces thereof.

While the resin film 1 is made of a material which is flexible, i.e.,bendable in the case of the above described embodiment, the resin film 1can be made of a rigid material such as a glass epoxy prepreg, anaramid-epoxy prepreg.

Also, a BT resin, a PPO, a PPE and the like can be used as the materialfor forming the above described resin film 1.

Next, the manufacturing process of the multilayer wiring board assemblycomponent as described above will be explained with reference to FIG.18.

At first, as illustrated in FIG. 18(a), a single sided copper platedresin film 10 is provided or prepared as the resin film 1 made of athermoplastic polyimide film having a thickness of 15 to 100 micrometerwith the copper foil 2 having a thickness of 5 to 18 micrometer bondedto one surface.

Next, as illustrated in FIG. 18(b), a dry film (resist) 4 is laminatedto the copper foil 2 bonded to the resin film 1 with a vacuum laminatoror a roll laminator.

Next, as illustrated in FIG. 18(c), the dry film 4 is exposed toradiation of a circuit pattern followed by developing the dry film 4.

Next, as illustrated in FIG. 18(d), a predetermined circuit pattern isformed by etching the copper foil 2 with the dry film 4 as a mask. Inthis step, the opening 5 is formed by the same etching process for usein the subsequent step of opening the through hole 7. Next, the dry film4 is removed from the copper foil 2 as illustrated in FIG. 18(e).

Next, as illustrated in FIG. 18(f), the first masking tape 6 a is bondedto the surface of the copper foil 2, which is attached to the resin film1 in the form of a circuit pattern, while the second masking tape 6 b isbonded to the surface of the resin film 1. The first and second maskingtapes 6 may be made of a PET and the like.

Next, as illustrated in FIG. 18(g), the through hole 7 of 0.05 to 0.3 mmdiameter is opened in the resin film 1 through the resin film 1 and thefirst and second masking tape 6 a and 6 b by exposing them to a laserlight by means of a CO₂ laser and the like corresponding to the opening5. Meanwhile, the through hole 7 may be opened by means of a drill inplace of the laser exposure process.

In this case, since the through hole 7 is formed through the opening 5by means of a CO₂ laser, it is possible to open a smaller hole (50 to250 micrometer diameter). Namely, if the through hole 7 were formedthrough the copper foil 2 in which the opening 5 had not be formed inadvance, a CO₂ laser (capable of opening holes of 50 to 250 micrometerdiameter) is not used for this purpose and therefore a larger hole of200 micrometer diameter or larger has to be opened by means of a drill(capable of opening holes of 200 micrometer diameter or larger).Meanwhile, some other lasers such as a UV-YAG laser, an excimer lasermay be used for this purpose of opening small holes. However, theselasers is too expensive to use for this purpose and therefore notpractical.

Meanwhile, since the through hole 7 as described above is passed alsothrough the copper foil 2, there are not generated voids, smear, as wellas the like drawbacks, which are likely if the conductive paste filler14 is embedded with the copper foil 2 as it is.

Next, as illustrated in FIGS. 18(h) and (i), the conductive paste 14 isplaced on the first masking tape 6 a and spread to fill the through hole7 therewith by moving a squeezee 15 made of an urethane, silicone andthe like in the direction of arrow A. At this time, a breathableseparate paper 31 as siliconized or fluoridized is placed for thepurpose of preserving the conductive paste 14 at the leading end of thethrough hole 7 near the resin film 1.

In this case, the separate paper 31 is provided with breathability forthe purpose of enabling air to escape when the through hole 7 is filledwith the conductive paste 14. Also, at least the upper surface of theseparate paper 31 is siliconized or fluoridized as described above forthe purpose of making easy to remove the separate paper 31 from theconductive paste filler 14 in contact with the separate paper 31 andpreventing the conductive paste filler 14 from being detached from thethrough hole 7 when the separate paper 31 is removed.

Meanwhile, Ag, Cu, C, Cu coated with Ag and other conductive pastes canbe used to form the conductive paste filler 14.

Next, the first projection 14 c of the conductive paste filler 14 whichis projecting through the upper surface 2 c of the copper foil 2 andhaving a diameter equal to or smaller than the diameter of the throughhole 7 is formed, as well as the second projection 14 b of theconductive paste filler 14 which is projecting from the resin film 1through the rare surface opposed to the printing surface and having adiameter equal to or smaller than the diameter of the through hole 7, asillustrated in FIG. 18(j), by removing the separate paper 31 and heatingthe conductive paste filler 14 in an oven at 80° C. to partially curethe conductive paste filler 14 and removing the first and second maskingtapes 6 a and 6 b. By this process, the multilayer wiring board assemblycomponent 20′ is completely formed.

Generally speaking, in the case where a land surface is formed on thecopper foil by the use of a metallic mask, the alignement of themetallic mask with holes of the substrate has to be achieved withsufficient precision such that it is necessary to excessively increasethe diameter (the land diameter) of the brim of the conductive pastefiller for securing the alignement.

Contrary to this, in accordance with the embodiments of the presentinvention as described above, the multilayer wiring board assemblycomponent is formed by bonding the masking tape 6 a on the copper foil2, opening a through hole through the masking tape 6 a and the copperfoil 2, removing the masking tape 6 a to form the first projection 14 c.A plurality of such multilayer wiring board assembly components arelaminated together in order that the first projection 14 c is crushedand spread on the copper foil 2 to form the brim (land) without need forexact accurate alignment while it becomes possible to adjust thediameter of the brim (land) by changing the thickness of the maskingtape 6 a.

Next, the press step for manufacturing a multilayer wiring boardassembly by joining a plurality of the multilayer wiring board assemblycomponents 20 as described above will be explained with reference toFIG. 19 and FIG. 20.

As illustrated in FIG. 19, a plurality of circuit patterns and aplurality of through holes 7 are formed on each of the multilayer wiringboard assembly components (three multilayer wiring board assemblycomponents) 20 a, 20 b and 20 c. Also, the through holes 7 are filledwith the conductive paste fillers 14.

The formation of the multilayer wiring board assembly in accordance withthe present embodiment is completed by laminating together therespective multilayer wiring board assembly components 20 a to 20 c bythermocompression with a most outer copper foil 9 at the same time orsequentially as illustrated in FIG. 20(a) and forming a circuit on themost outer copper foil 9 as illustrated in FIG. 20(b). The step oflaminating the respective multilayer wiring board assembly components 20a to 20 c and the most outer copper foil 9 to each other bythermocompression is carried out by heating them at 280° C. orthereabout and pressing them at 9 MPa or thereabout in order to embedthe circuit pattern of the copper foil 2 and brims 14 a of theconductive paste filler 14 in the resin film 1 made of a thermoplasticpolyimide having adhesivity and fluidity. At this time, the conductivepaste fillers 14 of the respective multilayer wiring board assemblycomponents 20 a to 20 c are fixedly pressed and finally cured bythermocompression at the same time.

In accordance with this embodiment as described above, since the throughholes 7 of the multilayer wiring board assembly component 20 a to 20 care filled with the conductive paste fillers 12, it is possible to makethe interlayer interconnection between each adjacent layers byvia-on-via. Also, since the projection 14 b of the conductive pastefiller 14 is formed in the printing surface, it becomes easy to make theelectric connection between the conductive paste fillers 14 having goodelectric connectivity when the interlayer interconnection is made byvia-on-via.

In this case, as illustrated in FIG. 20(a), the first projection 14 c ofthe above described multilayer wiring board assembly component 20′ issquashed by compression of the conductive paste filler 14 as describedabove to form the brim 14 a having a diameter larger than that of thethrough hole 7 and laterally extending on the copper foil 2 beyond theperimeter of the through hole 7 in order to increase the contact area ofthe conductive paste filler 14 with the copper foil 2 resulting inimproved electric connectivity.

The step of laminating the respective multilayer wiring board assemblycomponents and the outer copper foil 9 to each other bythermocompression is carried out by heating them at 280° C. orthereabout and pressing them at 9 MPa or thereabout.

In accordance with this embodiment as described above, since the firstprojection 14 c of the above described multilayer wiring board assemblycomponent 20′ is squashed by compression of the conductive paste filler14 to form the brim 14 a having a diameter larger than that of thethrough hole 7 and laterally extending on the copper foil 2 beyond theperimeter of the through hole 7 resulting in improvement of electricconnectivity.

Furthermore, since the copper plated resin film 10 is used in themanufacturing process of the multilayer wiring board assembly component,it becomes easy to preserve the accuracy of alignment of dimensions andpositions when holding a sample, opening a hole and filling the holeand, as a result, it is possible to save labor in the manufacturingworks. Namely, in the case of a conventional case, the respective stepsof holding a sample, opening a hole and filling the hole have to beconducted with a resin film 1 (the polyimide film) having a smallthickness as it is. However, in accordance with this embodiment, therespective steps of holding a sample, opening a hole and filling thehole are conducted after bonding the copper foil 2 to the resin film 1and therefore it becomes easy to open and fill holes with the conductivepaste fillers 12.

Furthermore, since a desired multilayer wiring board assembly can beformed only by preparing multilayer wiring board assembly components asdescribed above and combining and joining them together, the press stepof a multilayer wiring board assembly becomes easy without need forconducting press steps of multilayer wiring board assembly components.

As explained heretofore, in accordance with the present invention, it ispossible to easily laminate together flexible FPCs having highly packingdensities by via-on-via and chip-on-via.

Also, in accordance with the present invention, the contact area of aconductive paste filler with a copper foil is increased when compressionbonding multilayer wiring board assembly components to each other, andtherefore it is possible to improve electric connectivity.

Next, with reference to FIG. 21, FIG. 22 and FIG. 23, a multilayerwiring board assembly component and the multilayer wiring board assemblyin accordance with a still further embodiment of the present inventionwill be explained.

In the case of this embodiment, the resin film 1 having adhesivity ofthe embodiment as illustrated in FIG. 1, FIG. 2 and FIG. 3 is made of athermosetting resin (3A).

In the case utilizing a thermoplastic polyimide as the resin film 1having adhesivity, the multilayer lamination (finally curing) is carriedout at a temperature not lower than the glass transition temperature.However, since there occurs degradation of conductive resin components(the conductive paste) and oxdization of metallic fillers because of theheating process for multilayer lamination, the thermoplastic polyimidehas to be made of a material selected among from those having lowerglass transition temperatures.

However, the modulus of elasticity of a thermoplastic polyimide islowered by heating and recovered again by cooling. Namely, athermoplastic polyimide has a characteristic that the modulus ofelasticity is reversible relative to the temperature change.Accordingly, in the case where a thermoplastic polyimide having a lowglass transition temperature is used as a resin film having adhesivity,there sometime occurs peeling-off during a soldering process aftermanufacturing the multilayer wiring board assembly, during a heatresistant test and so forth. It is therefore inevitable to use amaterial having a higher glass transition temperature.

Accordingly, in order to solve the above described dilemma encounteredwhen a thermoplastic polyimide is used, it is required that thepolyimide resin film 1 can be compression bonded at a low temperaturewhile maintaining the heat resistant feature of the polyimide.

For this purpose, the interlayer resin film 1A having adhesivity isformed by the use of a heat resistant resin such as a thermosettingresin (which is not hardened (uncured) in an initial state, and hardened(cured) at a temperature higher than the cure temperature while theinitial state can not be recovered, even if cooled, as maintaining thehardened state) rather than the use of a thermoplastic adhesivematerial. It is therefore possible to manufacture a multilayer wiringboard assembly having a good heat resisting property with little damageto the respective boards during the manufacturing process by selectingthe cure temperature of the thermosetting resin to be lower than thetemperature at which the resin contained in the conductive paste is notdamaged and the filler is not oxidized.

Namely, the multilayer wiring board assembly component 20 is aconnection unit for use in the process of laminating a multilayer wiringboard assembly and comprises an FPC as a base element made of a singlesided copper plated resin film. Namely, as illustrated in FIG. 21(j),the multilayer wiring board assembly component 20 is composed of acopper plated resin film 10 composed of a resin film 1A made of athermosetting polyimide and provided with a copper foil 2 bonded to onesurface thereof, and a conductive paste filler 12 embedded in a throughhole 7 (refer to FIG. 21(g)) passed through the resin film 10 to form aninner via hole. A predetermined circuit pattern is formed in the copperfoil 2 by etching and the like. The conductive paste filler 12 isembedded in the through hole 7 from the surface of the copper foil 2 byscreen printing and so forth and laterally extending on the uppersurface of the copper foil 2 as a brim 12 a beyond the perimeter of theopening thereof with the printing surface 12 c of the conductive pastefiller 12 being flat and flush therewith in order that the leading endthereof is projected as a projection 12 b through the opposed surface ofthe copper plated resin film 10 having the resin film 1A.

While the resin film 1A is made of a material which is flexible, i.e.,bendable in the case of the above described embodiment, the resin film1A can be made of a rigid material such as a glass epoxy prepreg, anaramid-epoxy prepreg.

Also, a BT resin, a PPO, a PPE and the like can be used as the materialfor forming the above described resin film 1A.

Also, the above described the resin film 1A is preferably made of aresin which is cured at 60° C. to 250° C.

Namely, the resin film 1A is preferably made of a resin whose the curetemperature is no higher than the heat resisting temperature of a resincontained in the conductive paste and no lower than the evaporationtemperature of the volatile component that is mixed into the conductivepaste.

A multilayer wiring board assembly is laminated by stacking a pluralityof the multilayer wiring board assembly components as illustrated inFIG. 21(j) (three units in the case of the embodiment as illustrated inFIG. 22 and FIG. 23). As illustrated in FIG. 22 and FIG. 23, since thethrough hole 7 of the multilayer wiring board assembly component isfilled with the conductive paste filler 12, it is possible to makeinterlayer connection via-on-via.

In this manner, when the interlayer interconnection is made byvia-on-via, the conductive paste fillers 12 are connected directly toeach other rather than through an intervening copper foil therebetweenas explained in the description of “BACKGROUND OF THE INVENTION”.

Next, the manufacturing process (method) of the multilayer wiring boardassembly in accordance with the present invention will be explained withreference to FIG. 21 through FIG. 23.

(1) The Manufacturing Process of a Multilayer Wiring Board AssemblyComponent (FIG. 21):

At first, as illustrated in FIG. 21(a), a single sided copper platedresin film 10 is provided or prepared as the resin film 1A made of athermosetting polyimide film and the like having a thickness of 15 to100 micrometer with the copper foil 2 having a thickness of 5 to 18micrometer bonded to one surface.

Next, as illustrated in FIG. 21(b), a dry film (resist) 4 is laminatedto the copper foil 2 bonded to the resin film 1A with a vacuum laminatoror a roll laminator. Next, as illustrated in FIG. 21(c), the dry film 4is exposed to radiation of a circuit pattern followed by developing thedry film 4.

Next, as illustrated in FIG. 21(d), a predetermined circuit pattern isformed by etching the copper foil 2 with the dry film 4 as a mask. Inthis step, the opening 5 is formed by the same etching process for usein the subsequent step of opening the through hole 7. Next, after thedry film 4 is removed from the copper foil 2 as illustrated in FIG.21(e), a masking tape 6 having a thickness of 10 to 50 micrometer isbonded as a mask to the surface of the resin film 1A as illustrated inFIG. 21(f). The masking tape 6 may be made of a PET and the like.

Next, as illustrated in FIG. 21(g), the through hole 7 of 0.05 to 0.3 mmdiameter is opened in the resin film 1 through the resin film 1A and themasking tape 6 by exposing them to a laser light through the opening 5by means of a CO₂ laser and the like. Meanwhile, the through hole 7 maybe opened by means of a drill in place of the laser exposure process.

In this case, since the through hole 7 is formed through the opening 5by means of a CO₂ laser, it is possible to open a smaller hole (50 to250 micrometer diameter). Namely, if the through hole 7 were formedthrough the copper foil 2 in which the opening 5 had not be formed inadvance, a CO₂ laser (capable of opening holes of 50 to 250 micrometerdiameter) is not used for this purpose and therefore a larger hole of200 micrometer diameter or larger has to be opened by means of a drill(capable of opening holes of 200 micrometer diameter or larger).Meanwhile, some other lasers such as a UV-YAG laser, an excimer lasermay be used for this purpose of opening small holes. However, theselasers is too expensive to use for this purpose and therefore notpractical.

Meanwhile, since the through hole 7 as described above is passed alsothrough the copper foil 2, there are not generated voids, smear, as wellas the like drawbacks, which are likely if the conductive paste filler12 is embedded with the copper foil 2 as it is.

Next, as illustrated in FIGS. 21(h) and (i), the conductive paste 12 isplaced on the copper foil 2 and a mask 33 spread to fill the throughhole 7 therewith by moving a squeezee 32 made of an urethane, siliconeand the like in the direction of arrow A. At this time, a breathableseparate paper 31 as siliconized or fluoridized is placed for thepurpose of preserving the conductive paste 12 at the leading end of thethrough hole 7 near the resin film 1A.

In this case, the separate paper 31 is provided with breathability forthe purpose of enabling air to escape when the through hole 7 is filledwith the conductive paste 12. Also, at least the upper surface of theseparate paper 31 is siliconized or fluoridized as described above forthe purpose of making easy to remove the separate paper 31 from theconductive paste filler 12 in contact with the separate paper 31 andpreventing the conductive paste filler 12 from being detached from thethrough hole 7 when the separate paper 31 is removed.

At this time, the conductive paste filler 12 is screen printed with adiameter larger than the opening 5 (the through hole 7) by about 10% to50% so that part of the conductive paste remains on the upper surface ofthe copper foil 2 beyond the perimeter of the opening 5 thereof. By thisconfiguration, there is formed the brim 12 a which is connected to theland surface 2 a of the copper foil 2 in the direction normal to thesurface. In this case, however, the printing surface 12 c of theconductive paste filler 12 is made flat.

Meanwhile, Ag, Cu, C, Cu coated with Ag and other conductive pastes canbe used to form the conductive paste filler 12.

Also, while the conductive paste filler 12 is formed by screen printingas described above, another suitable printing technique is used for thispurpose.

Next, after removing the separate paper 31, the projection 12 b of theconductive paste filler 12 which is projecting through the resin film 1Ain the surface opposed to the printing surface is formed by heating theconductive paste filler 12 in an oven at 80° C. partially cure theconductive paste filler 12 and removing the masking tape 6 asillustrated in FIG. 21(j). In this case where the resin film 1A ispartially cured at the partial curing temperature of 80° C., it is madeof a resin which can be finally (irreversibly) cured at a temperaturehigher than the partial curing temperature of 80° C. Meanwhile, it ispossible to dispense with the partial curing process (for dissipatingthe solvent and air) when the conductive paste filler 12 is made of sometype of a conductive paste.

By this process, the multilayer wiring board assembly component 20 iscompletely formed.

(2) The Press Process of the Multilayer Wiring Board Assembly (FIG. 22and FIG. 23):

As illustrated in FIG. 22, a plurality of circuit patterns and aplurality of through holes 7 are formed on each of the multilayer wiringboard assembly components (three multilayer wiring board assemblycomponents) 20 a, 20 b and 20 c. Also, the through holes 7 are filledwith the conductive paste fillers 12.

The formation of the multilayer wiring board assembly in accordance withthe present embodiment is completed by laminating together, at a time orsuccessively, the respective multilayer wiring board assembly components20 a to 20 c by thermocompression with a most outer copper foil 9 asillustrated in FIG. 23(a) and forming a circuit on the most outer copperfoil 9. The step of laminating the respective multilayer wiring boardassembly components 20 a to 20 c and the most outer copper foil 9 toeach other by thermocompression is carried out by heating them at 170°C. or thereabout and pressing them at 9 MPa or thereabout in order toembed the circuit pattern of the copper foil 2 and the brim 12 a of theconductive paste filler 12 in the resin film 1A made of a thermosettingpolyimide. At this time, the conductive paste fillers 12 of therespective multilayer wiring board assembly components 20 a to 20 c arefixedly pressed and finally cured by thermocompression at the same time.

In accordance with this embodiment as described above, since theinterlayer resin film 1A having adhesivity is formed by the use of aheat resistant resin such as a thermosetting resin (which is nothardened (uncured) in an initial state, and hardened (cured) at atemperature higher than the cure temperature while the initial state cannot be recovered, even if cooled, as maintaining the hardened state)rather than the use of a thermoplastic adhesive material, it is possibleto manufacture a multilayer wiring board assembly having a good heatresisting property with little damage to the respective boards duringthe manufacturing process by selecting the cure temperature of thethermosetting resin to be lower than the temperature at which the resincontained in the conductive paste is not damaged and the filler is notoxidized. Also, since the volatile component of the conductive pastefiller is evaporated in genral at 100° C. or thereabout, the resin film1A is made of a resin which is cured at a temperature not lower than theevaporation temperature.

Furthermore, since the through holes 7 of the multilayer wiring boardassembly component 20 a to 20 c are filled with the conductive pastefillers 12, it is possible to make the interlayer interconnectionbetween each adjacent layers by via-on-via. Also, since the projection12 b of the conductive paste filler 12 is formed in the printingsurface, it becomes easy to make the electric connection between theconductive paste fillers 12 having good electric connectivity when theinterlayer interconnection is made by via-on-via.

Still further, since the conductive paste filler 12 is embedded in thethrough hole 7 during printing operation in order that the printingsurface thereof is laterally extended from the opening 5 of the copperfoil 2, the brim 12 a of the conductive paste filler 12 makes reliableelectric contact with the inner side surface and the upper surface ofthe copper foil 2 beyond the perimeter of the opening 5 thereof, andtherefore it is possible to connect the copper foil 2 to the conductivepaste filler 12 without compromising the electric connectivity betweenthe copper foil 2 and the fillers of the conductive paste.

Still further, since the copper plated resin film 10 is used in themanufacturing process of the multilayer wiring board assembly component,it becomes easy to preserve the accuracy of alignment of dimensions andpositions when holding a sample, opening a hole and filling the holeand, as a result, it is possible to save labor in the manufacturingworks. Namely, in the case of a conventional case, the respective stepsof holding a sample, opening a hole and filling the hole have to beconducted with a resin film (the polyimide film) having a smallthickness as it is. However, in accordance with this embodiment, therespective steps of holding a sample, opening a hole and filling thehole are conducted after bonding the copper foil 2 to the resin film 1Aand therefore it becomes easy to open and fill holes with the conductivepaste fillers 12.

Furthermore, since a desired multilayer wiring board assembly can beformed only by preparing multilayer wiring board assembly components asdescribed above and combining and joining them together, the press stepof a multilayer wiring board assembly becomes easy without need forconducting press steps of multilayer wiring board assembly components.

Next, with reference to FIG. 24, FIG. 25 and FIG. 26, a multilayerwiring board assembly component and the multilayer wiring board assemblyin accordance with a still further embodiment of the present inventionwill be explained.

In the case of this embodiment, the resin film 1 having adhesivity ofthe embodiment as illustrated in FIG. 1, FIG. 2 and FIG. 3 is made of athermoplastic polyimide to which is given a thermosetting property (1B).

When a thermoplastic polyimide is used as the resin film 1 havingadhesivity, the multilayer lamination (finally curing) is carried out ata temperature not lower than the glass transition temperature. However,since there occurs degradation of conductive resin components (theconductive paste) and oxdization of metallic fillers because of theheating process for multilayer lamination, the thermoplastic polyimidehas to be made of a material selected among from those having lowerglass transition temperatures.

However, the modulus of elasticity of a thermoplastic polyimide islowered by heating and recovered by cooling again. Namely, athermoplastic polyimide has a characteristic that the modulus ofelasticity is reversible relative to the temperature change.Accordingly, in the case where a thermoplastic polyimide having a lowglass transition temperature is used as a resin film having adhesivity,there sometime occurs peeling-off in a soldering process aftermanufacturing the multilayer wiring board assembly, in a heat resistanttest and so forth. It is therefore inevitable to use a material having ahigher glass transition temperature.

Accordingly, in order to solve the above described dilemma in the use ofa thermoplastic polyimide, it is required that the resin film 1 can becompression bonded at a low temperature while maintaining the heatresistant feature of the polyimide.

For this purpose, the interlayer resin film 1 is formed of athermoplastic polyimide 1B to which is given a thermosetting property,and therefore it is possible to manufacture a multilayer wiring boardassembly having a good heat resisting property without damaging theconductive resin components (the conductive paste).

Namely, the multilayer wiring board assembly component 20 is aconnection unit for use in the process of laminating a multilayer wiringboard assembly and comprises an FPC as a base element made of a singlesided copper plated resin film. Namely, as illustrated in FIG. 24(j),the multilayer wiring board assembly component 20 is composed of acopper plated resin film 10 composed of a resin film 1 having adhesivityand made of a thermoplastic polyimide (TPI) and provided with a copperfoil 2 bonded to one surface thereof, and a conductive paste filler 12embedded in a through hole 7 (refer to FIG. 24(g)) passed through theresin film 10 to form an inner via hole. A predetermined circuit patternis formed in the copper foil 2 by etching and the like. The conductivepaste filler 12 is embedded in the through hole 7 from the surface ofthe copper foil 2 by screen printing and so forth and laterallyextending on the upper surface of the copper foil 2 as a brim 12 abeyond the perimeter of the opening thereof with the printing surface 12c of the conductive paste filler 12 being flat and flush therewith inorder that the leading end thereof is projected as a projection 12 bthrough the opposed surface of the copper plated resin film 10 havingthe resin film 1B.

While the resin film 1B is made of a material which is flexible, i.e.,bendable in the case of the above described embodiment, the resin film1B can be made of a rigid material such as a glass epoxy prepreg, anaramid-epoxy prepreg

Meanwhile, a BT resin, a PPO, a PPE and the like can be used as thematerial for forming the above described resin film 1B.

Also, the resin film 1B is made of a thermoplastic polyimide to which isgiven a thermosetting property having a cure temperature of 150° C. to200° C., a modulus of elasticity of 600 to 1400 MPa and a glasstransition temperature of 70° C. to 90° C.

A multilayer wiring board assembly is laminated by stacking a pluralityof the multilayer wiring board assembly components as illustrated inFIG. 24(j) (three units in the case of the embodiment as illustrated inFIG. 25 and FIG. 26). As illustrated in FIG. 25 and FIG. 26 since thethrough hole 7 of the multilayer wiring board assembly component isfilled with the conductive paste filler 12, it is possible to makeinterlayer connection via-on-via.

In this manner, when the interlayer interconnection is made byvia-on-via, the conductive paste fillers 12 are connected directly toeach other rather than through an intervening copper foil therebetweenas explained in the description of “BACKGROUND OF THE INVENTION”.

Next, the manufacturing process (method) of the multilayer wiring boardassembly in accordance with the present invention will be explained withreference to FIG. 24 through FIG. 26.

(1) The Manufacturing Process of a Multilayer Wiring Board AssemblyComponent (FIG. 24):

At first, as illustrated in FIG. 24(a), a single sided copper platedresin film 10 is provided or prepared as the resin film 1 made of athermoplastic polyimide film to which is given a thermosetting propertyand having a thickness of 12.5 to 50 micrometer with the copper foil 2having a thickness of 5 to 18 micrometer bonded to one surface.

Namely, in this case, a polyimide base bonding sheet made of athermoplastic polyimide to which is given a thermosetting property istemporarily compression bonded, as the resin film 1B, under a pressureof 40 kgf/cm² for a short time (about 10 minutes) at a temperaturehigher than the glass transition temperature (70 to 90° C.) and lowerthan the cure temperature (when finally cured) during the press process(the lamination process) of the multilayer wiring board assembly asexplained in the following description.

In this case, the polyimide base bonding sheet 1B as the above describedthermoplastic polyimide to which is given a thermosetting property canbe formed, for example, with a polyimide base bonding sheet selectedamong from the SPB series distributed by Nippon Steel Chemical Co., Ltd.Meanwhile, the manufacturing method of a polyimide base bonding sheetselected among from the SPB series distributed by Nippon Steel ChemicalCo., Ltd. and other necessary information is disclosed in JapanesePatent Application No. Hei 10-37700 (Japanese Patent PublishedApplication No. Hei 11-228825) filed in Feb. 19, 1998 and JapanesePatent Application No. Hei 10-145872 (Japanese Patent PublishedApplication No. Hei 11-335555) filed in May. 27, 1998.

Next, as illustrated in FIG. 24(b), a dry film (resist) 4 is laminatedto the copper foil 2 bonded to the resin film 1B with a vacuum laminatoror a roll laminator. Next, as illustrated in FIG. 24(c), the dry film 4is exposed to radiation of a circuit pattern followed by developing thedry film 4.

Next, as illustrated in FIG. 24(d), a predetermined circuit pattern isformed by etching the copper foil 2 with the dry film 4 as a mask. Inthis step, the opening 5 is formed by the same etching process for usein the subsequent step of opening the through hole 7. Next, after thedry film 4 is removed from the copper foil 2 as illustrated in FIG.24(e), a masking tape 6 having a thickness of 10 to 50 micrometer isbonded as a mask to the surface of the resin film 1B as illustrated inFIG. 24(f). The masking tape 6 may be made of a PET and the like.

Next, as illustrated in FIG. 24(g), the through hole 7 of 0.05 to 0.3 mmdiameter is opened in the resin film 1 through the resin film 1 and themasking tape 6 by exposing them to a laser light through the opening 5by means of a CO₂ laser and the like. Meanwhile, the through hole 7 maybe opened by means of a drill in place of the laser exposure process.

In this case, since the through hole 7 is formed through the opening 5by means of a CO₂ laser, it is possible to open a smaller hole (50 to250 micrometer diameter). Namely, if the through hole 7 were formedthrough the copper foil 2 in which the opening 5 had not be formed inadvance, a CO₂ laser (capable of opening holes of 50 to 250 micrometerdiameter) is not used for this purpose and therefore a larger hole of200 micrometer diameter or larger has to be opened by means of a drill(capable of opening holes of 200 micrometer diameter or larger).Meanwhile, some other lasers such as a UV-YAG laser, an excimer lasermay be used for this purpose of opening small holes. However, theselasers is too expensive to use for this purpose and therefore notpractical.

Meanwhile, since the through hole 7 as described above is passed alsothrough the copper foil 2, there are not generated voids, smear, as wellas the like drawbacks, which are likely if the conductive paste filler12 is embedded with the copper foil 2 as it is.

Next, as illustrated in FIGS. 24(h) and (i), the conductive paste 12 isplaced on the copper foil 2 and the mask 33 and spread to fill thethrough hole 7 therewith by moving a squeezee 32 made of an urethane,silicone and the like in the direction of arrow A. At this time, abreathable separate paper 31 as siliconized or fluoridized is placed forthe purpose of preserving the conductive paste 12 at the leading end ofthe through hole 7 near the resin film 1B.

In this case, the separate paper 31 is provided with breathability forthe purpose of enabling air to escape when the through hole 7 is filledwith the conductive paste 12. Also, at least the upper surface of theseparate paper 31 is siliconized or fluoridized as described above forthe purpose of making easy to remove the separate paper 31 from theconductive paste filler 12 in contact with the separate paper 31 andpreventing the conductive paste filler 12 from being detached from thethrough hole 7 when the separate paper 31 is removed.

At this time, the conductive paste filler 12 is screen printed with adiameter larger than the opening 5 (the through hole 7) by about 10% to50% so that part of the conductive paste remains on the upper surface ofthe copper foil 2 beyond the perimeter of the opening 5 thereof. By thisconfiguration, there is formed the brim 12 a which is connected to theland surface 2 a of the copper foil 2 in the direction normal to thesurface. In this case, however, the printing surface 12 c of theconductive paste filler 12 is made flat.

Meanwhile, Ag, Cu, C, Cu coated with Ag and other conductive pastes canbe used to form the conductive paste filler 12.

Also, while the conductive paste filler 12 is formed by screen printingas described above, another suitable printing technique is used for thispurpose.

Next, after removing the separate paper 31, the projection 12 b of theconductive paste filler 12 which is projecting through the resin film 1Bin the surface opposed to the printing surface is formed by heating theconductive paste filler 12 in an oven at 80° C. partially cure theconductive paste filler 12 and removing the masking tape 6 asillustrated in FIG. 24(j). By this process, the multilayer wiring boardassembly component 20 is completely formed.

(2) The Press Process of the Multilayer Wiring Board Assembly (FIG. 25and FIG. 26):

As illustrated in FIG. 25, a plurality of circuit patterns and aplurality of through holes 7 are formed on each of the multilayer wiringboard assembly components (three multilayer wiring board assemblycomponents) 20 a, 20 b and 20 c. Also, the through holes 7 are filledwith the conductive paste fillers 12.

The formation of the multilayer wiring board assembly in accordance withthe present embodiment is completed by laminating together, at a time orsuccessively, the respective multilayer wiring board assembly components20 a to 20 c by thermocompression with a most outer copper foil 9 asillustrated in FIG. 26(a) and forming a circuit on the most outer copperfoil 9. The step of laminating the respective multilayer wiring boardassembly components 20 a to 20 c and the most outer copper foil 9 toeach other by thermocompression is carried out by heating them at 180°C. or thereabout and pressing (finally compression bonding) them at 40kgf/cm² for 60 minutes or thereabout in order to embed the circuitpattern of the copper foil 2 and the brim 12 a of the conductive pastefiller 12 in the resin film 1B made of a thermoplastic polyimide havingadhesivity and fluidity. At this time, the conductive paste fillers 12of the respective multilayer wiring board assembly components 20 a to 20c are fixedly pressed and finally cured by thermocompression at the sametime.

During the final compression bonding process, the conductive resincomponents (the conductive paste 12) shall not be deteriorated since theheating temperature is as low as 180° C.

Also, in this case, the multilayer wiring board assembly is not curled(warped). Namely, while the resin film having adhesivity is contractedor expanded during heating, the contraction or expansion can becancelled out if there is a center line of symmetry in the cross sectionthereof. However, a polyimide film is a highly flexuous material andtherefore tends to be curled (warped) when heated. However, since theheating temperature can be set as low as about 280 to 180° C. inaccordance with this embodiment, no curl (warp) appears.

As detailedly explained in the above, in accordance with thisembodiment, the resin film 1B having adhesivity is made of athermoplastic polyimide base bonding sheet to which is given athermosetting property so that it is possible to manufacture amultilayer wiring board assembly without deteriorating the conductiveresin components (the conductive paste) and without forming curl (warp).

Also, since the through holes 7 of the multilayer wiring board assemblycomponent 20 a to 20 c are filled with the conductive paste fillers 12,it is possible to make the interlayer interconnection between eachadjacent layers by via-on-via. Furthermore, since the projection 12 b ofthe conductive paste filler 12 is formed in the printing surface, itbecomes easy to make the electric connection between the conductivepaste fillers 12 having good electric connectivity when the interlayerinterconnection is made by via-on-via.

Furthermore, since the conductive paste filler 12 is embedded in thethrough hole 7 during printing operation in order that the printingsurface thereof is laterally extended from the opening 5 of the copperfoil 2, the brim 12 a of the conductive paste filler 12 makes reliableelectric contact with the inner side surface and the upper surface ofthe copper foil 2 beyond the perimeter of the opening 5 thereof, andtherefore it is possible to connect the copper foil 2 to the conductivepaste filler 12 without compromising the electric connectivity betweenthe copper foil 2 and the fillers of the conductive paste.

Still further, since the copper plated resin film 10 is used in themanufacturing process of the multilayer wiring board assembly component,it becomes easy to preserve the accuracy of alignment of dimensions andpositions when holding a sample, opening a hole and filling the holeand, as a result, it is possible to save labor in the manufacturingworks. Namely, in the case of a conventional case, the respective stepsof holding a sample, opening a hole and filling the hole have to beconducted with a resin film (the polyimide film) having a smallthickness as it is. However, in accordance with this embodiment, therespective steps of holding a sample, opening a hole and filling thehole are conducted after bonding the copper foil 2 to the resin film 1Band therefore it becomes easy to open and fill holes with the conductivepaste fillers 12.

Furthermore, since a desired multilayer wiring board assembly can beformed only by preparing multilayer wiring board assembly components asdescribed above and combining and joining them together, the press stepof a multilayer wiring board assembly becomes easy without need forconducting press steps of multilayer wiring board assembly components.

Meanwhile, the profiles of the through hole 7 and the conductive pastefillers 8 and 12 of the multilayer wiring board assembly component 20 asillustrated in FIGS. 1(i), 7(j), 8(j), 9(e), 12(j), 15(k), 18(j), 21(j)and 24(j) are usually circles as horizontally viewed (i.e., as viewedfrom above in FIGS. 1(i), 7(j), 8(j), 9(e), 12(j), 15(k), 18(j), 21(j)and 24(j)). While the present invention is not limited to thoseembodiments, other profiles are possible. As detailedly explained in theabove, in accordance with the present invention, a through hole isopened through the copper plated resin film made of a resin film havingadhesivity which is provided with a copper foil bonded to one surfacethereof, and filled with a conductive paste, and therefore it becomeseasy to form the through hole and embed the conductive paste because ofthe increase in thickness as compared with the case where a through holeis opened only through a resin film and filled with a conductive paste.

Also, in accordance with the present invention, the conductive pastefiller of the multilayer wiring board assembly component is embedded inthe through hole of the copper plated resin film by screen printing witha leading end of the conductive paste filler being projected from theresin film, and therefore it is possible to make reliable electricconnection of the leading end of the conductive paste filler with thecopper foil or the conductive paste filler of the multilayer wiringboard assembly component and to improve electric connectivity betweenthe respective layers when a plurality of the multilayer wiring boardassembly components are laminated together. Particularly, in this case,direct connection between the conductive paste fillers without theintermediary copper foil is effective to improve the electricconnectivity.

As explained heretofore, in accordance with the present invention, it ispossible to easily laminate together flexible FPCs having highly packingdensities by via-on-via and chip-on-via.

Furthermore, since the resin film having adhesivity is made of athermosetting resin in accordance with the present invention, it ispossible to manufacture a multilayer wiring board assembly having a goodheat resisting property with little damage to the respective boardsduring the manufacturing process.

Furthermore, the resin film having adhesivity is formed of athermoplastic resin to which is given a thermosetting property inaccordance with the present invention, and therefore it is possible tomanufacture a multilayer wiring board assembly having a good heatresisting property without damaging the conductive resin components (theconductive paste).

Meanwhile, the resin film having adhesivity can be made of, for example,a thermoplastic resin such as a thermoplastic polyimide. In this case,the respective adjacent multilayer wiring board assembly components arefixedly joined by means of the resin film which is made soft bylaminating the multilayer wiring board assembly components together andheating them, and therefore it is possible to make reliable electricconnection of the conductive paste filler with the copper foil and theconductive paste filler of the adjacent multilayer wiring board assemblycomponent. Also, in this case, smooth electrical connection can beachieved by finally curing the conductive paste filler at the same timeas the multilayer wiring board assembly components are laminatedtogether.

Furthermore, when a multilayer wiring board assembly component islaminated, it is preferred that the copper foil as the outermost layeris embedded in the resin film to which it is bonded. Namely, in thistype of the multilayer wiring board assembly, plating is performed withgold and the like, taking into consideration the connection between anIC and the connection member such as solder and protection of thecircuit from oxidation. However, when the circuit is exposed, theentirety of the electrode pattern including the sides has to bemetallized to require much gold. Also, since the sides of the electrodepattern are metallized, the width of the circuit is increased making itdifficult to form micropatterns and also increasing the rate ofoccurence of defective connections due to contamination of metallicimpurities between circuits. Furthermore, if electrode patterns areclosely located to each other, the plating solution is not uniformlyapplied making it difficult to uniformly perform the plating process.

At this point, since the copper foil as the outermost layer is embeddedin the resin film, the side walls of the electrode pattern is notperformed so that it is possible to reduce the amount of gold asrequired, to advance the miniaturization of circuits, to improve uniformapplication of the plating solution, and to prevent occurence ofimperfect insulation due to contamination.

The foregoing description of the embodiments has been presented forpurposes of illustration and description. It is not intended to beexhaustive or to limit the invention to the precise form described, andobviously many modifications and variations are possible in light of theabove teaching. The embodiment was chosen in order to explain mostclearly the principles of the invention and its practical applicationthereby to enable others in the art to utilize most effectively theinvention in various embodiments and with various modifications as aresuited to the particular use contemplated.

1. A multilayer wiring board assembly laminated with a plurality ofmultilayer wiring board assembly components, being manufactured by amethod comprising: preparing a plurality of multilayer wiring boardassembly components comprising; a resin film having adhesivity, a copperfoil bonded to one surface of the resin film, a through hole openedthrough the copper foil and the resin film, and a conductive pasteembedded in the through hole so as to have a projection projectedoutward from the resin film; and laminating the multilayer wiring boardassembly components with the other of the multilayer wiring boardassembly components such that the projection of the conductive paste ispressed against the conductive paste or the copper foil of an adjacentone of the multilayer wiring board assembly components, all of thecopper foil and the conductive paste are filled in the resin film,wherein the projection of the conductive paste is in close contact withthe conductive paste or the copper foil of the adjacent one of themultilayer wiring board assembly components in order to make theelectric connection having good electric connectivity.
 2. The multilayerwiring board assembly as claimed in claim 1, wherein the conductivepaste is embedded in the through hole with part of the conductive pastebeing laterally extending beyond the perimeter of the opening of thethrough hole of the copper foil.
 3. The multilayer wiring board assemblyas claimed in claim 1, wherein the resin film is made of a thermoplasticadhesive.
 4. The multilayer wiring board assembly as claimed in claim 1,wherein the resin film is a resin film having adhesivity and fluidity.5. The multilayer wiring board assembly as claimed in claim 1, whereinthe laminating of the multilayer wiring board assembly components withthe other of the multilayer wiring board assembly components is carriedout by heating.
 6. The multilayer wiring board assembly as claimed inclaim 1, wherein the conductive paste are fixedly pressed and finallycured by thermocompression at the same time.